Huh! Maybe it's lens foreshortening or something, but they look huge in the picture.
Anyways, back on topic, that's a really cool project, mate! I have a friend who spends hundreds of dollars per pair of shoes to get boutique style Converse like these.
You should clean your walls now that you've got a sick design like that!
I usually use the generic magic erasers. They work with friction so you don't need water, but sometimes it helps.