Update: revamped the configuration to get rid off the GRE intermediate incapsulation. Unfortunately, ipsec VPN speed still stays around 1.5 MBit/sec.

show chassis hardware:

emz@LDN-MX5> show chassis hardware 
Hardware inventory:
Item             Version  Part number  Serial number     Description
Chassis                                XXXXX             MX5-T
Midplane         REV 10   711-038215   XXXXXXXX          MX5-T
PEM 0            Rev 05   740-028288   XI00424           AC Power Entry Module
PEM 1            Rev 05   740-028288   XI00409           AC Power Entry Module
Routing Engine            BUILTIN      BUILTIN           Routing Engine
TFEB 0                    BUILTIN      BUILTIN           Forwarding Engine Processor
  QXM 0          REV 06   711-028408   XXXXXXXXX         MPC QXM
FPC 0                     BUILTIN      BUILTIN           MPC BUILTIN
  MIC 0                   BUILTIN      BUILTIN           4x 10GE XFP
    PIC 0                 BUILTIN      BUILTIN           4x 10GE XFP
  MIC 1          REV 02   750-061622   XXXXXXXX          MS-MIC-16G
    PIC 2                 BUILTIN      BUILTIN           MS-MIC-16G
FPC 1                     BUILTIN      BUILTIN           MPC BUILTIN
  MIC 0          REV 30   750-028392   XXXXXXXX          3D 20x 1GE(LAN) SFP
    PIC 0                 BUILTIN      BUILTIN           10x 1GE(LAN) SFP
      Xcvr 0     REV 02   740-013111   B302483           SFP-T
      Xcvr 1     REV 02   740-013111   B302729           SFP-T
      Xcvr 2     REV 02   740-013111   F172228           SFP-T
    PIC 1                 BUILTIN      BUILTIN           10x 1GE(LAN) SFP
      Xcvr 0     REV 02   740-013111   B261212           SFP-T
      Xcvr 1     REV 02   740-013111   F380617           SFP-T
      Xcvr 2     REV 02   740-013111   F150924           SFP-T
      Xcvr 3     REV 02   740-013111   B304909           SFP-T
Fan Tray                                                 Fan Tra

configuration, important pieces:

chassis {
    fpc 0 {
        pic 0 {
            tunnel-services {
                bandwidth 1g;
            }
            inline-services {
                bandwidth 1g;
            }
        }
        pic 2 {
            adaptive-services {
                service-package layer-3;
            }
        }
    }
    alarm {
        management-ethernet {
            link-down ignore;
        }
    }
}
services {
    service-set nat-lan {
        nat-rules default;
        interface-service {
            service-interface ms-0/2/0;
        }                               
    }
    service-set tcp-mss {
        tcp-mss 1343;
        service-set-options {
            enable-asymmetric-traffic-processing;
        }
        stateful-firewall-rules permit-all;
        interface-service {
            service-interface ms-0/2/0.3;
        }
    }
    service-set ipsec-srx-perm {
        next-hop-service {
            inside-service-interface ms-0/2/0.4;
            outside-service-interface ms-0/2/0.5;
        }
        ipsec-vpn-options {
            local-gateway 93.179.66.1;
        }
        ipsec-vpn-rules srx-perm;
    }
    ipsec-vpn {
        rule ipsec {
            term 1 {
                from {
                    source-address {
                        172.16.6.1/32;
                    }
                    destination-address {
                        172.16.6.0/32;
                    }
                }
                then {
                    remote-gateway 91.196.139.1;
                    dynamic {
                        ike-policy ike-policy;
                        ipsec-policy ipsec-policy;
                    }
                    initiate-dead-peer-detection;
                }
            }
            match-direction input;      
        }
        rule srx-perm {
            term default {
                from {
                    ipsec-inside-interface ms-0/2/0.4;
                }
                then {
                    remote-gateway 91.196.139.1;
                    dynamic {
                        ike-policy ike-policy;
                        ipsec-policy ipsec-policy;
                    }
                    copy-dont-fragment-bit;
                    initiate-dead-peer-detection;
                    dead-peer-detection {
                        interval 10;
                        threshold 5;
                    }
                }
            }
            match-direction input;
        }
        ipsec {
            proposal ipsec-proposal {
                protocol esp;
                authentication-algorithm hmac-sha1-96;
                encryption-algorithm aes-128-cbc;
            }
            policy ipsec-policy {
                perfect-forward-secrecy {
                    keys group2;
                }
                proposals ipsec-proposal;
            }
        }
        ike {
            proposal ike-proposal {
                authentication-method pre-shared-keys;
                dh-group group19;
                authentication-algorithm sha-256;
                encryption-algorithm aes-128-cbc;
                lifetime-seconds 14400; 
            }
            policy ike-policy {
                proposals ike-proposal;
                local-id ipv4_addr 93.179.66.1;
                pre-shared-key ascii-text "$9$oQZiqmPQz3/24F/CuIRhSrKX-wsgoJDlKx-VboaGDiHqf0OR"; ## SECRET-DATA
            }
        }
        establish-tunnels immediately;
    }
    stateful-firewall {
        rule permit-all {
            match-direction input-output;
            term accept {
                then {
                    accept;
                }
            }
        }
    }
    nat {
        pool pool-default {
            address 93.179.66.3/32;
            port {
                automatic;
            }
        }
        rule default {
            match-direction input;
            term no-nat {
                from {
                    destination-address {
                        10.0.0.0/8;
                        192.168.0.0/16;
                        172.16.0.0/12;
                    }
                }
                then {
                    no-translation;
                }
            }
            term default {
                from {                  
                    source-address {
                        10.10.116.0/24;
                        10.10.102.0/23;
                    }
                }
                then {
                    translated {
                        source-pool pool-default;
                        translation-type {
                            napt-44;
                        }
                    }
                }
            }
        }
    }
}
interfaces {
    ms-0/2/0 {
        unit 0 {
            family inet;
        }
        unit 1 {
            family inet;
            service-domain inside;
        }
        unit 2 {
            family inet;
            service-domain outside;
        }
        unit 3 {
            description "TCP MSS Modification";
            family inet;
            family inet6;
        }
        unit 4 {
            description "SRX, Perm";    
            family inet {
                mtu 1383;
                service {
                    input {
                        service-set tcp-mss service-filter mss-filter;
                    }
                    output {
                        service-set tcp-mss service-filter mss-filter;
                    }
                }
                address 10.200.200.17/32 {
                    destination 10.200.200.16;
                }
            }
            family inet6;
            service-domain inside;
        }
        unit 5 {
            family inet;
            family inet6;
            service-domain outside;
        }
    }