Any Dell Inspiron 7559 4k laptop users experiencing Windows 10 desktop animation / video playback lag should make some noise here:
I picked up one of these laptops a few weeks ago, and the Nvidia GTX 960M GPU performs like a champ when it comes to 1080p gaming and video editing. However, the Intel HD 530 side, which handles Windows 10’s desktop animations, chokes on very basic tasks like window animations and video playback (both standard and high-definition). There’s word on the Interwebs that this is either an issue with Intel’s HD 530 graphics driver optimizations, or else is related to the way Windows 10 handles graphics acceleration for legacy desktop apps vs. Modern / Universal Windows Platform (UWP) apps. Or maybe none of the above.
The bottom line: if you’ve got a 7559 4k and are experiencing a similar issue, post at the aforementioned link. Hopefully with enough awareness raised, Dell and / or Intel will be able to get rid of the lag once and for all.