This is great, and has a lot of potential to reduce confusion and chargebacks. You can do a lot of things with 15 dynamic characters, including putting in base32 unique codes and URLs.

Another really useful example of creative use of the descriptor comes from 37signals' blog from 2009. They put a URL in the descriptor and reduced chargebacks 30%:

http://signalvnoise.com/posts/1545-how-we-reduced-chargeback...