Being a tile based game is heavily CPU intensive, and yeah I feel you. I have an i7 8750h and 1060 on my laptop that can play VR games perfectly yet I generally consider myself running fast when I get 30fps in this game... To the point I have a hard time driving the cars when the frame rate is actually good and the cars suddenly go much faster.
The irony is my old 4770k and 760 with 6gb ram handle the game good.
I found that I sometimes get the low frames and it doesn't go away so a quick quit and rejoin seems to fix it. Going from 4fps back to like 16 is nice when you know you aren't in an area that should be causing it.
Remove any major game impact mods that take up large space (yes that means britas) and slowly add mods in to see what changes performance.
Hopefully the next release is good and does away with the majority of tile stuff.
PS don't have a lot of stuff on the floor. My base is pretty slow on my server because of all the stuff everywhere but in a fresh game it handles well.