With the same game settings performance is essentially the same for cinema mode and full VR. If there is a difference at all, cinema mode performance can be a tiny little bit worse with the “Lounge” scene due to the extra 3D environment. It’s purposefully super-low-poly though, so that shouldn’t really be noticable usually.
Depending on how close you move the cinema screen, you can get away with a lower game resolution in cinema mode though while still having a decent pixel density. So if you don’t move the screen too close and reduce the game resolution compared to what you would use for full VR, performance sometimes can be better in cinema mode. That’s solely due to the lower game resolution though, not because of cinema mode.