After your save file reaches 15MB, it is game over.
However, the game is broken, especially for the PS3 version. Once you reach a save file with a size of 10-15 MBs, the game is practically unplayable with 0 framerates per second (fps). There are also many glitches and numerous quest bugs that make the game a nuisance at times. Dragons flying backwards, no magic resistance, many game-stopping quest bugs and similar other issues cause significant distress for you throughout the game. You could find a way around all these glitches maybe, especially with future patches, but its seems like the lag will not (cannot) be solved in the future, which is a pity.
You should either wait and hope that Bethesta solves the fps problem with future patches and purchase a used/GOTY copy in a couple of months, or you should just stay away from the game all together. You are very likely to love the game for the first 30 hours of gameplay, and hate and be frustrated with it after that.