There are some reports of speed issues in 2015.6, specially with Nvidia GTX cards.
If you want, you can roll back to 2015.5.1 until it's fixed. Here's how: http://www.lightroomqueen.com/how-do-i-roll-back-to-lightroom-2015-1-1-or-lightroom-6-1-1/
Simply replace 6.1.1 with 6.5.1
Thanks for your reply! I´ve read all those comments, but IMO that´s a different problem. People reported a general slowdown, which is not the case on my system.
I won´t roll back, just hope for a fix. This bug ísn´t a dealbreaker, "just" annoying.
It can be due to a (confirmed) memory leak in 2015.6.
If it still works for you, OK. I assume a fix is on its way.
Wouldn´t a memory leak mean that my RAM is maxxed out and the application has to use the HDD?
If yes, that´s not the case here. I´ve enough RAM left (about 20GB).
BTW. to give an example:
At start, GPU usage is about 15% while I drag the exposure slider. After a few minutes it goes down to 3% and I get a jerky screenredraw, by far not as smooth as at the beginning.
Are you doing a lot of brushing or spot healing on photos?
No, very, very seldom!
And the slowdown is even in totally unedited images. I guess, LR looses some kind of "connection" to the GPU.