There’s no practical way to accelerate this today, and the current process is sequential, CPU-bound, and limited to a couple of threads.
You can speed it up - slightly - by making fewer thumbnails:
Big Media folder? Make smaller video preview thumbnails!
And usually only video codec keyframes are extracted; I’ve seen reports that changing this can make it faster. That’s not intuitive to me, but you could test it. Maybe big CPUs like yours can muscle through it!
See this for instructions, and the next message about it being faster for another user:
Video Preview Thumbnail Generation Fails for Some Items - #48 by Volts
If you felt absolutely crazy, it would be possible to generate the VPT thumbnail files using external scripts. 
