It's strange. The movement of the soldiers is very slow only on the upper levels of the base. But if the soldiers run at the lower levels, the speed is standard. The movement speed of the soldiers is very different. Apparently precisely because the map is multilevel.
I'm just trying to figure out if anyone has a similar situation.
Everybody has this problem.
Some people tolerate it better, some less so.
The underlying engine is too detailed and there are just too many calculations, regardless of how powerful your PC is.
Options you have:
1. (player) use simpler display mode
2. (player) use lower resolution
3. (modder) use smaller maps
4. (modder) use standard visibility ranges, lighting mode and similar settings