Here you got the screenshots, note the JF is turned off, and is a really demanding plane when you tuned it on due to the screens and all the lights it has.
In VR fps are really important, when FPS vary in VR the user can suffer sickness, and thats not Good:(
Other planes Works with higher FPS, that's why I speak about the cockpit, because I think that there's the problem.
PS: I know that FPS may vary between aircrafts, maybe something between 4-5 FPS, but having 10, or even more than 10 FPS difference is quite a hard hit in VR.