I am trying to implement a wave-based enemy system for my base-building game and I want there to be a higher enemy count around 75-150 enemies. However, around 30 enemies my game starts to lag REALLY bad (around 5-10 fps). I’ve checked if it is the mesh colliders or rigid bodies, but that does not improve the performance at all. They are animated objects with 20 bones and a blender amateur animation, and I don’t think that the script can be causing it, for it only moves the enemies forward. Why are they lagging? Have I truly hit my limit?
Hard to answer. It depends a lott of your Graphics card, secondly free system memory.
I tested my own settlers style game with 200 NPCs few month ago, with Geforce
7xx series card I haven’t problem.
This kind of game:
With my laptop intel HD graphic, it ruined totally 
If you move your NPCs directly with c#, direction and height, (no dynamic force etc…) you may try to disable your rigidbody totally and see it that helps. If so, you can always put your NPC in kinematic, do not use gravity mode, when moving it By C# script. It is possible that your C# scrip fights with enabled physics… Profiler will tell you what is the problem.