Hmm, it runs smoothly here on my pretty-old and weak macbook pro (13″ 11,1).
So, let’s try one thing at a time. First, just open bella_gui, enable IPR without changing anything, and let me know if navigating the camera in the default scene gives you beachball & lag.
If that seems OK, then let’s proceed to import FBX, but just make a simple one for testing, and see how that behaves. If that’s OK, then I’ll request to see the FBX you are referring to above, in case there is something peculiar about it that is producing lag.