Rendering empty scene (solid color) in Unity 2019.1.10f takes Quest's GPU around 10ms. After further profiling I discovered that there are 4 render textures (I'm guessing color and depth for each eye) and that they take almost 300MB of space.
Snapdragon Profiler showed that texture memory read is often up to 6.25 MB/s. Profiling the game with Renderdoc didn't show any huge textures, eye textures were taking around 13.07MB (1216x1344) What could be the cause of this?