Below are two responses from Kent from the CGC discord about this topic and how to fix it:
"If
you're wondering how you ended up at 25 mil at the "same level 6" as
me, it all depends on the polycount of the retopology. Your retopo is
higher poly than mine in the video and each subdiv level quadruples the
count.
Awkwardly your level 5 is only 7m which isn't quite as high as needed for crisp pore details.
To
fix optimize this I would recommend deleting the multires, and increase
your polycount on the retopo slightly (by cutting a few new edges loops
and evening out adjacent loops). Mathematically the goal would be to
end up between 12-17M polies once you subdivide up to level 5.
If
you don't want to do that, I'd try to get away with your level 5 right
now (7M). 25 mil is going to be a huge time waster when you do test
renders (edited)
I only have 32 GB of RAM so I'm not even going to attempt it. Yikes."
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