There is a big difference in update latency in "camera preview" when trying to move a camera in the scene in contrast to the "implicit" camera used in regular interaction. I have reported this before (in the 1.7 series) But it used to crash the system so that ended the tests at that time. Now it is a performance issue instead.
The goal is to be able to frame a camera shot while RPR renders the preview in the same way one can quickly rotate the regular preview.
As it is now, I can spin around a scene with descent performance in the regular way (shift-Z, then MMB etc) but when I want to place a camera interactively the view updates many times slower and this makes it unusable.
I have tried to get around this by moving in an OpenGL view and having the RPR view separate but it has the same effect. The only thing that works is to revert to OpenGL preview when placing the camera and then doing a quick f12 production rendering "old school style".