UPDATE: This does not happen on the E175. Only the E195 so far.
I have loaded this plane in various places with various scenery complexities, and just sitting at a gate or rolling down a taxiway without touching any flight controls, I get 30+ FPS regardless and I'm happy with that situation. But turning the plane on a taxiway, or doing a flight control check, or trying to maintain centerline on takeoff, the second I move the joystick in any way, the FPS immediately drops to 7 or less and the plane is unusable, and then about two seconds later after I haven't touched anything, the FPS returns to it's normal, high, usable value. AP commands do not affect FPS.
I use a Logitech extremepro3D.
2x GTX 1080 SLI
64GB RAM at 3000Mhz
subject line edit by mods - added Logitech to description as this is possibly a controller specific issue and not users-wide; subject line noting issue solved with work-around discussed in the thread.