How to understand the balance between large and small number of polygons in IOS GA models?

Question

3D

I'm making a runner for IOS, I can't understand the balance between a large and small number of polygons in one model. I would like to make all the game models better and more presentable, but I don’t understand how much I can detail the model so that the phones do not die during the loading of the scene. Still tormented by the question of the specifics of the calculation of angles and polygons. Do they count together or each model separately? Good people, help with advice.