Virtual reality with Android/Trinus, slowing down FPS

I did a VR test with Andoird/Trinus connected to my PC, as it seems an affordable alternative to Oculus Rift.
In my game I made head-tracking mouse dependent, for being controlled by Trinus.
I tested with Wifi as well as with USB-Tethering.

Everything works fine, except that my FPS have dropped drastically !

Streamers like Trinus are supposed to pass on frames to the phone, the same way as when streaming a video. We are not talking about stereo imaging here. So in my opinion Trinus does't do anything more than just streaming video to the phone.
I therefore don't understand at all what is going on here. Average FPS falls back from 35 to 12 when using Trinus.
Has anyone a technical explanation for this ?? Anyone with a similar same experience ?