There were a couple of cases in early 2017 where users were finding with the old Windows SDKs and the older SR300 camera model that their camera speed was capped at 17 FPS no matter what resolution they tried or ample program they ran. A definitive cause was not identified though, and in one of those cases the problem fixed itself on its own.
There was a bug in early versions of SDK 2.0 that caused FPS to drop by 50%. The bug's reference name was DSO-7183. It was marked as fixed though in a subsequent version.
There were also a couple of rare cases where the FPS was being dragged down because the lighting in the room that the camera was being used was too dim. Is the lighting in the location where your camera is being used at a relatively normal level?