Scene complexity makes a huge difference in how well ME performs. If you have a really complicated build with a ton of blocks it tends to perform worse.
If you want to send me a save file, I can look at it, but definitely no promises -- I don't have a ton of time anymore. Probably upload somewhere else and post a link here, check the private box if you don't want to publicly share the save.

If a near empty scene performs at 10-15fps that would be very shocking to me. There are two settings that might contribute to that, Extreme voxel and model quality. Both are rarely playable, and I'd suggest not putting those above High unless you're trying to take a screenshot.

I don't know if this is your problem, but let me share a similar experience of mine.

I have upgraded my PC as well. I now have an AMD R7 7700x and a 4070 12GB. However the game did not seem to use the 4070 at all.
Then I went into the "Gaming" tab in "Windows Settings" and then "Graphics" and in the list of apps there I set the game to "High performance" which listed my GPU next to it.

That's when it started working much better!

If your cpu has an internal GPU then windows will default the game to that one. The above steps are the solution SHOULD this be your problem!

I hope this helps!

Sorry correction I meant:

the "Gaming" tab in "Windows Settings", then Game Mode and THEN "Graphics"