Optimization

Optimization is incredibly important for VRChat. Being in VR, it should run at a high frame rate so the users can play the game comfortably. I’ve experienced countless times when my friends or I had to quit because we were feeling too nauseous.

Keeping this number as low as possible without terribly sacrificing quality is the balancing act you will have to perform in developing content for this game. Reducing the number of polygons is done through decimation; in Blender this is mostly done through the decimate modifier.

Each material slot incurs a draw call on the CPU. Ideally on an avatar or 3D model you will have 1 material slot per differently shaded part.
Merging multiple material slots into 1 is done through texture atlasing. This can be automated in the CATS Blender Plugin.

 Setting Up For Quest Creation[docs.vrchat.com]