Are you sure? I remember reading 23/2 was. Ah, either way, they're both beautiful pieces. I've played through 32/10 a few times over the past couple days. I'd like to learn both 23/2 and 32/10 but I'll probably do 32/10 in the near future since it's not technically that difficult, I don't think. 23/2 didn't seem terrible either, except the left hand endurance required.
I saw an interview of a pianist who's name I can't remember, and he played Op 32 10 in a concert. He said that Rachmaninoff was like, 'Dude you're so awesome man! Thanks for playing my favorite prelude, you're so rad man!' *fist bump afterwards*
I'll have to find it of course...