That's one of the many reasons I tell people to use c2. My game, loot pursuit, takes somewhere around 3-5 minutes to preview. CC caches the graphics after the first preview, which speeds it up a little for consecutive previews as long as all you changed was code.
Having big images in particular makes it take a lot longer to preview. I reduced the preview time in my game quite a bit by loading large background images at runtime instead via the sprite's 'load frame from file' action.
Edit: oh, you already are loading them at runtime. Sorry, but I don't know any other tricks to speed up preview time. :/