I'm running Mavericks, on a MacPro with lots of ram, and Photoshop CC 2015 is very slow, and un responsive. It sometimes will not respond to tool change clicks, and will continue a lasso outside of frame and into the interface - ignoring much...
Tool changes sounds a bit like a Wacom driver bug from several months ago, fixed in a driver update.
The selection drawing incorrectly is a known bug in CC 2015 when GPU drawing is disabled -- we're testing a fix for that now.
But without more information, we can't know why your system is running slow.
It could be due to a third party plugin or extension panel, or corrupt fonts (try turning off font preview), some problem with network connectivity, or the known issue with rulers drawing slowly (also testing a fix for that).