I just let Adobe CC upgrade my Lightroom 5.7 to Lightroom CC and once I got past that little glitch about needing to log all the way out of Adobe CC and log back in to get it to start I'm very pleasantly surprised by it's increased speed. I have a decent graphics card and Lightroom CC is obviously making good use of that now (I'd imagine with just the on-board graphics that I wouldn't see much improvement).
I have one photo in particular where I went way way overboard with the adjustment brush to the point that (with Lightroom 5.7) it would drag my system to a screeching halt whenever I tried to zoom or pan. I experimented with that same photo in Lightroom CC and the speed of these actions is actually reasonable now (of course I wish they were even faster, but compared to before it's an amazing difference).

