Hi everyone,
Today I manage to play 4 hours straight whitout lag and or almost freeze bug. I simply update my PS3 from 3.70 to 3.73 and I disable all the automatic save in game.
Also, I delete all my auto save. I have 34+ hours of gameplay, at level 24 and my save file is 9.5 mb in size.

Maybe you can try by yourself and see if it work for you.

Hope it help you!!

And I should add that loading time between doors are a little faster whitout auto save.

Try it!