Unity Mobile depth buffer problem

I'm a junior game developer, we are developing a mobile MMO game with Unity 5.2.4.

Recently i'm trying to do an performance optimization. I tried to render the static scene stuffs into a render target with color buffer and depth buffer, with w$$anonymous$$ch i render to the following frames before the dynamic objects are rendered if the game main player's viewpoint stays the same. My goal is to reduce some draw calls as well as to save some power for mobile devices. T$$anonymous$$s strategy saves up to 20% power in our MMO mobile game consumption on android devices. It works on iphone/ipad and PC platform as expected, However it do not work on Android. Here is my question on StackOverflow. We use Unity 5.2.4. https://stackoverflow.com/questions/50171517/unity-mobile-depth-buffer-precision

Do anyone have idea about t$$anonymous$$s ? Thanks