Many people have reported this bug. This topic in the official Adobe feedback forum describes some workarounds that worked for others: Lightroom 2015.2:Hangs on quit. Please add your vote and details about your issue to that bug report, to help Adobe understand the scope of the issue. By following that topic, you'll receive updates on the issue.
That does seem to have fixed it.
The first Quit after making that change, it hung. Had to Force Quit.
But then subsequent launches and Quits were working.
BTW, the "Apply auto tone Adjustments" in Presets preferences, mentioned in Feedback Forum, was already unchecked.