Zero problems with lag on our various 15.6 machines (laptops, desktops), be it a dedicated video player or browser.
.
That information would be helpful:
a - what type of app(s) are showing lag?
b - what type of video files are played?
websites?
c - Has this lag been since the original 15.6 install
Or since an update?
d - Did you install afresh, or upgrade from 15.5?
a. VLC, MPV and Haruna all experience lag
b. All my movies are MP4 1080p Blu-ray
c. I just used openSUSE Leap 15.6 for the first time
d. Fresh install and not upgrade
I would recommend running ‘top’ and ‘nvtop’ concurrently while playing a video, and observe the CPU and GPU loading. That might help identify the issue a little more specifically.