I've been practicing the octave tremelos (written as 64ths) In Lingua Mortua for three years. I've built them up gradually to at least 32's . I think I'm doing eight per quarter note in the other hand. 64ths would be sixteen.
I'm both rotating the wrist a little and wiggling fingers one and five, sounds like the advice above. Wrist is straight to the forearm.
This speed of learning doesn't line up with the conservatories piece a month or whatever miracles they require of the students, but my progress is positive. So be patient, if I can do it, you can. I'm age 63.
It takes a lot of strength, and while I don't slow down at the end, I do miss a few notes after I am tired.
Take heart, if you get the strength to do this on Pathetique, you have the most difficult part of another piece down already.