do you have all the nulls selected while AE was this slow, and are you sure there is no keyframes on the position of the layers even if they dont move. I dont know with nulls from Maya, but when i translate nulls over from Softimage, all translation parameters are keyframed every frame even if they are not keyframed in Softimage.
You probably already checked this, but just asking, because i also find AE to slow very quickly to a crawl if you select some 3d nulls/layers with keyframes on every key, even if the keyframed parameter is not exposed in the timeline.
Orbiting a camera with no null/layers selected is really smooth and fast, selecting 1 null/layer with keyframes on every frame slows AE down noticable, 2 nulls/layers with this even more so, 3-4 getting laggy, 200 layers like this? several seconds delay doing anything.
This might be what you experience too in this scene? just a thought.