I want to build a game for android. In the game you can collect coins. These coins has the same material. In the binging of the game I create enough coin and I put them into a pool so I can use them when they are needed without using instantiate and destroy continuously. How can I reduce the number of the draw calls? I cannot combine them into one mesh or can I?
In theory, you could create all your coins out of a single mesh, but before you go to those lengths, make sure your coins are batching, and then test the result on your target platform. You can see in the stats if your coins are batching. To batch 1) the coin mesh needs to have less than 900 vertex attributes, and 2) you need to not make any changes to the material on the coins at runtime. The number of vertex attributes will depend on how the mesh is defined, but typically you need to get under 300 vertices to get under 900 vertex attributes.
Once you have them batching, run a test on the target device. Keep instantiating coins until you see a slow down. Experiment a bit with simpler shaders to see how much the shader is impacting your performance.