Not to knock you, but if they wanted to demo it for a studio session length then 15 minutes is a pretty limiting amount of time. VSTs have varying quality, take a while to learn the workflow, tons of features and are very expensive. It's like Photoshop, but you have no idea if it will be useful to you.

Kanye is probably bad with money, but he remembers what it's like to be a poor musician.

If you haven't already come out at him outraged, maybe you can talk to him about your product and get some good publicity. Or start a temporary 'Kanye' discount and offer it to him first.