Turning the textures down to 25 or so helps alot of its memory related. I'd also suggest turning off shadows and pixel shaders. Also, your desktop resolution determines your game resolution, so lower your desktop resolution to improve performance as well. And try moving your battle size slider all the way to the left, makes the battles smaller, i.e. less of a strain on your PC. But more importantly, as Nairagorn asked, what are your system specs? If you have a good system it's possible that you're experiencing a bug of some sort.