In unity it is called Occlusion Culling, only stuff in the camera view is rendered, it is not enabled by default but it is built in, just adding a few objects, changing a few settings and pressing a bake button. I set it up and baked the occlusion culling as well as baked the scene lighting, I am sure there are other ways to optimize the game, but I just can't think of them at the moment. I guess pausing the AI movement calculation if they are beyond a certain distance from the player, but tracking the distance to each cat from the player might add to the issue as much as it fixes. Definitely worth testing though.