I am using the latest iPad Pro 11in with iPadOS 15.4 and Illustrator could not possibly move any slower when vectorizing images. Once the vectorizing is done, I then expand it which only "processes" half of the time. Followed up by me trying to select from the 1B vectors created for whatever obscene reason to edit and take away in order to actually access the figure I wanted vectorized in the first place. Anyone else having a hard time with the vectorization process??
I have a 4th gen iPad Pro. A full color photo takes about 8-10 seconds. Every time you change settings it has to re-run that process, so that adds time, which is typical. Less complex art takes less time. Is it still slow for you when you try vectorizing a black and white line drawing? You might also try airplane mode, so Illustrator isn't trying to save to the cloud as you are working - I'm not sure, but that may help. Then when you reconnect it can save your work.
Also if you give it full color art it traces every color, every shade, so yes you have a billion paths. Try the logo setting, try lowering the number of colors. It may still be very complex, but that depends on the art you give it.