Every new update of LR significantly reduces performance. Every photo correction with sliders in developer view costs 2-3 seconds to show up the result with enabled GPU. If I turn the GPU support off the "Tint" slider manipulation freezes LR for 5-6 seconds before i can see the result.
I am using iMac 27 Late 2013 with 16 Gigs of RAM. Every update makes my work slower and slower again. I want to roll back to older versions, because Adobe are killing their product year by year. I simply cannot work in LR.
And yes, the LR CC 2015.2.1 update didn't fix import crash bug. It is really insane!
I would request you to please wait for an upcoming update that should take care of these issues.
Meanwhile please Roll Back to the previous version : https://helpx.adobe.com/lightroom/kb/roll-back-to-prior-update.html
What is update release date?
As of now there is no date, however it should be there at the earliest.