How can I make AI NPC characters less laggy?

I am working on an AI restaurant game, which involves a lot of NPC customers walking around. This often gets laggy. I already have a script that limits the amount of NPCs that can be in the game, but they often get laggy. Does anyone know of a way to make these less laggy?

I am looking for, possibly, a script that disables animations when the player is far away, or just runs animations on the client. Any ideas?