I too think that your image files are too large. I have a very fast internet connect here at work and it too longer for the sample page to load than I would expect for images of that size. Anything over 1MB for an image file is huge. Perhaps another format would work better, like .jpg/.jpeg.

I was looking through my cache and I noticed that some of the sample picture files are less that 0.5MB. If you could get all of the images to that size I think you'd be golden.