It is an issue being discussed in a few threads at the 'other site'. Slowness as you describe isn't all that out of the ordinary, responding to the remote is also an issue.
At the moment, my 3 HR24s are fast enough to not be very irritating, but the remote response issue is getting more prevalent and more irritating. There are lots of pointers to fixes, none of which work with any regularity. Reset NVRAM, clear cache, reduce # of recordings kept on the HD. All mentioned with nearly no consistency of what causes or fixes the issue.
The fix will come if and when D* decides speed of operation and remote response is as important as adding trivial things like TV Apps, Pandora and YouTube. Unfortunately, imo, I don't think that day has arrived yet. From my POV, I would switch back to the old SDGUI in a heartbeat on my HR24s. With it, my HR24s were nearly as snappy in operation as was my 722k from Dish.