I still have it every day with four or five processes I think. It always happens only once a day. And they are always the same, photolibraryd, coreduetd, IMDPersitenceAgent, corespotlightd and imagent is there too, but not so extreme like the others.
They always go crazy together and after a few times (I think three is enough) force quitting them in Activity Monitor they are going back to normal and while I do this BiomeAgent is going up too and I quit it also a few times.
I am on 15.1 Beta 5 and I think it startet in Beta 3 und was gone in 4. Could also have started earlier and I just didn't notice it because I only saw it because of System Monitor or iStatMenu and don't know when I had one of those installed.
They also only went all a little over or near 100. So alltogether maybe 400-500% and that didn't slow anything down. I just noticed the very silent fan when it had been quiet and the recognized, the iMac got very hot in the middle of the big bottom bezel. I rebooted but it came back immediately.
And I am doing almost nothing when that happens, less then now, and now they look like this:
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So they are doing nothing. I should note the time when it happens, to see if it's always the same.
Just updated again to overwrite everything with the full installer a few days ago, but that didn't help.