using only STP protocol, no NVE etc should be used, is it feasible
No, it is not possible at all. If you need that kind of solution, you have to have a direct connection between these two locations. It is not a practical solution and therefore you have to use an ISP connection. But you do not need your own router and you can config ISP router based your requirements. L2VPN is also a good solution and it is easy to configure. MPLS is great solution for your problem and you can use the technologies below to achieve your goal.