Just to be clear, you need to play two different multi-minute sounds at once?
There's a library of long songs, and a library of short sound effects. There's never more than one long song playing at a time.
why don't you just preload the 3-second one into a pygame.mixer.Sound object and play it whenever you need it, and play the 13-minute one with pygame.mixer.music?
D'oh! Good idea, I'm embarrassed that I didn't think of it. Done and problem solved.