There is a Harder one later on route.
If you've already helped Rinny in Transylvania to investigate the manor, next time you sleep afterward will make a poster appear on the side of the Inn that mentions hypnosis.
Undergoing it yourself will give you +25% exp to anything you train (a minimum bonus of +1 exp as long as it gains any at all) until next time you sleep.
+4 instead of +3 doesn't sound like a lot, but trust me, it adds up really fast. Especially once you can quick travel to the slums to get a massage to gain your stamina back instantly for just 15 credits.
Alternatively, you can just bring lots of Angel Milk with you. 10 stamina recovery for such an easy to get item is pretty good. Which, funnily enough, is my most recommended strategy for raising Mysticism in the Succubus Tower library lol