I know you already mentioned that hot water by itself didn't get the peanut butter off in a timely fashion, but this answer involves using your fingers in addition to that to get it off a lot faster:

I eat a lot of peanut butter (Skippy Natural). One thing I've found that works for me, to avoid getting peanut butter on my washcloth, is to wipe off the peanut butter with my fingers under water (ideally hot) before I wash it. It comes off pretty easily from a knife or what-have-you, that way (and slips right down the drain, leaving just the oil on your fingers for you to wash off, which is much easier than dealing with it on a washcloth).

If the peanut butter has already dried, that might be a problem.

Also, using extra soap helps.

I know you already mentioned that hot water by itself didn't get the peanut butter off in a timely fashion, but this answer involves using your fingers in addition to that to get it off a lot faster:

I eat a lot of peanut butter (Skippy Natural). One thing I've found that works for me, to avoid getting peanut butter on my washcloth, is to wipe off the peanut butter with my fingers under water (ideally hot) before I wash it. It comes off pretty easily from a knife or what-have-you, that way (and slips right down the drain, leaving just the oil on your fingers for you to wash off, which is much easier than dealing with it on a washcloth).

If the peanut butter has already dried, that might be a problem.

Also, using extra soap helps if you if you it the traditional way.