I've used LR from it's inception and I've been running CC for quite some time—presently Vs. 2015.7 (Sierra 10.12.1 on a 2011 MacBook Pro with 8 GB RAM). Over the years, especially since I switched to CC, I've noticed startup taking longer and longer! It just took 4+ minutes for a folder of 20 images that I'd optimized yesterday, but I've seen it take much longer. I've optimized the catalogue over and over, but still no improvement.
Equally annoying—and I've experienced this with multiple versions much older than CC—the adjustment brush will cease to function and nothing works, except to quit and restart LR.
I'm curious as to what others are experiencing.