Love the 3d art design. Seems like all ZBrush sculpts? Serious skill.
Performance is a little bit rough even on a beast machine. In Unity you can mark all non-moving objects as Occludee Static and all large platforms/walls as Occluder Static. You can also mark all those same non-moving objects as Batch Static. That will likely help with most of your performance problems. If you want to dive 5x deep you can also go into baked lighting. It will bloat your file size if uncontrolled but your framerate will improve. There are many ways to improve framerate, that's just two of them. Good luck on your future developments!