Se honestly this is what porting processes are made for. You optimize the game to run on ps3 it's as simple as that.

The characters have so many poly's nobody would even notice if you reduce the polycount by 10 000 polys and lower the texture resolution on all surfaces.

Little big planet looks great but does it mean it can't be ported to psp? No. Why do you need me to tell you this anyway? You ported FFIII on the iphone!