Just ran on both the newest public beta 14.6.0(44) and shipping. On a project of 4k BRAW with a couple other layers of Lumetri and an adjustment layer with Lumetri.
No dropped frames, playback was fine. Quite an interesting color shift to that LUT also!
EDIT: on shipping version 15.5.0 (51) one of my Lumetri tabs was 'off'. With both instances of Lumetri with one running your Osiris LUT and the adjustment layer, I had some dropped frames. None even with everything on in the public beta.
Thanks again Neil - but dang, I'm at a bit of a loss here. Of course, I'm sure there can be a lot of reasons for why you can't reproduce the issue on your end. The differences between setups can turn into a long list pretty quickly. A few off the top of my head:
I'm running 4K monitors with scaling on. Is your laptop display hi res?
I haven't tested BRAW footage - only H.264, HEVC, and ProRes so far
I'm currently on Nvidia studio driver 456.71 but I'm fairly certain I already tried 452.06 when I was upgrading from 14.3.1 to 14.4. I've also tested 4 or 5 drivers overall and none of them have helped with this issue
I do have custom workspaces setup but again, I believe I've already tried reverting to one of the default layouts
I guess I'll do some more testing. If you have any suggestions on things to try, I'm all ears.
I did some further testing and wanted to report back that the 14.6 public beta has much better playback performance. From what I've experimented with so far, it doesn't exhibit the laggy/dropping frames issue at all - even with chunkier LUTs.
Just to confirm the issue didn't stem from something in my upgrade path or configuration of the regular version of Premiere, I also tried the 14.5 beta and the terrible playback returned. So it seems the only "solution" right now is to use the 14.6 beta, or wait for the 14.6 production release.