It is quite nice poster. There's a few scratches up on the top and there's a bent corner (bottom left) but really not in too bad condition realistically. It's a nice metal poster, too. I could imagine it is rare - I did a bit of googling and saw a lot of reproductions. I believe it is from the late 1930's as well. Really like it. Sometime soon I'll hang it up above my computer.
Oh and you are definitely right, $15 is an absolute steal. I imagine we got pretty lucky there!