Actually the issues at hand is not the complexity of the models as most are indeed extremely low-poly, but rather that the Unity Engine doesn't like having hundreds and hundreds of seperate gameObjects in the scene at once, even if they are just cubes that don't do anything. Once a four digits number is reached, frame rate starts to drop.
The original even had to make sure that only one other character was on screen along with the player, so I should be glad to have a little bit more power at my disposal
