Comment # 2 on bug 1127979 from Nicolas Patricio Saenz Julienne

(In reply to Stefan Dirsch from comment #1)
> I believe you have some strange limits configured for the monitor in your
> /etc/X11/xorg.conf. I suggest to remove this file completely and try again.
> 
> Apart from this Dell Precision 5520 is an Optimus system (Intel
> Kabylake/NVIDIA). Should work with NVIDIA GPU as rendering device with the
> help of suse-prime package now. We have it running here with sle15-sp1 Beta4
> on this machine.

That did it. Thanks! I'm using suse-prime BTW.