I am using a Macbook Pro and Lightroom 2015.6 as updated Friday. Since the update I have been experiencing increasing issues with freezes in the system and now I can not do anything at all. It will take 3 to 4 minutes just to open and then I can not do anything at all because as soon as I try it locks up the whole application. My mac OS is 10.10.5.
Please turn off the Graphics Processor from the Lightroom preferences.
Go to Lightroom Preferences from the Edit menu
Click on Performance tab
Uncheck the Graphics Processor
Let us know if that helps.