My suggestion would be to reduce your file size. Big files can massively impact performance, and an important part of running games on roll20 is managing limited resources. If its not a JPG, use an image program to convert it to jpg at say 90% quality, and you should be able to significantly reduce the size with no perceptible difference in visual quality. For some files, you might have to lower quality more - just dont reduce the quality of the same file over and over. Always make a copy of your original, and resave that one with lower and lower qualities to test it.
