I'm sorry, but this is not a solution. This is the worst rollout of a new feature-set since the invention of the square wheel. This latest update isn't getting us anywhere.
A number of people have reported this bug in the official Adobe feedback forum: Lightroom 2015.2: Hangs on quit. There are two workarounds that have worked for some in that topic:
- Uncheck Preferences > General > Show Add Photos Screen.
- Reset LR's preferences: Resetting the lightroom preferences file - updated - Lightroom Forums
Please add to that bug report your vote, details of your issue, and whether either of those two workarounds helped you. That will make it a little more likely Adobe will prioritize a fix.
Resetting Preferences and restarting my iMac seems to have resolved the problem. Thank you!