How to speed up unity 3D game?

I am creating COIN game, When there are many coin on scence my game is become slow. Is there any way to solve this problem

My guess is that you are instantiating coins, and they possibly do not share a material.

Some information on batching : Unity - Manual: Draw call batching

information on optimizing :

You should have all your coins in a pool then re-use your coins by adding them and removing them as required.

Here is some information on pooling :

You have possibly got a really high processing prefab or a really high polygon model in your game.