I couldnt find a place to suggest tips for you guys.
My personal freelance developer, said that i could try and write this to you:
"Please make your export utility take a hash of all the input graphics, and only run compression on each of them, if that image has been changed since last export. Should speed up the process tremendously"
I think he wants to be able to export faster on big image heavy projects!
That would mean, i will pay him less! Just a suggestion