Yep, after updating to AMD 15.7 Lightroom is constantly goes to "Not responding" on my R9 290x. Had to disable graphics processor acceleration to get it working. Update from Adobe on this situation would be appreciated.
Ditto with my R9 270. i7-4790K and 12GB of RAM.
I had the same problem with an AMD Radeon HD 7850 after updating to Catalyst 15.7.1. In the Develop module I would edit a photo, switch to another, and get an endless blue circle and "Not Responding" in the title bar. I also ran into the same lockup as OP when trying to uncheck Edit -> Preferences -> Performance -> "Use Graphics Processor". After editing the "Autobahn" property in the preferences file as recommended LR CC has been running without issue. Here's where to find the preferences file per Adobe: Preference file and other file locations | Lightroom 5
I'm running Windows 7 64 bit with an AMD FX-8350 and 16GB of RAM.
Great find OP!