In the example scene with the cube that emits particles, I get about 20~ fps with LG G3.
When I turn of distortion correction I get about 40~ fps.
I’m using Unity 5.1.2 and the newest Unity google cardboard package from github.
Any idea how to fix that?
Anyone?..
Bump!
the original shader that does distortion correction is realy heavyweight on mobile devices 
The trick I use to boost performance up about 30% (at least on my nexus 5, compared to original stereo one) is to do it by hand, render the two cameras (eyes) into textures (with eye shifting ofcourse), then have special meshes (distorted grids, say 10x10, (that basically with vertex color & shape mimic the pixel shader stuff)) in the third camera view - this is very ugly approach, but works, and is faster than original one.
Remember to use RGB565 as target textures for cameras (and use latest unity - as at some time 565 support on android was broken for a while (reported 565 but in reality was 8888 - again at least on nexus 5) - hope this helps
Thanks MXAdd! I already finished with my project but next time I will probably try your solution. too bad it has to be that tricky, If anyone else have an easier solution please let me know.