Is your ps3 connected in wireless? I found it slows down downloads a lot for me, so if it's the case I suggest trying with a cable.
I don't believe it's coming from a port issue since your download work, they're just slow. I suggest looking around for anything that hog up bandwith (torrent client on another pc for example).
I also have a 10mbps line (dsl), and I need roughly 30mn to grab a 1gb demo when my line is clear. So maybe you're far from a server or something, 1 1/2 hour is not an alarmingly low speed.
I hope you can solve it