I'm pretty sure 15% is the best public code out right now.
I got a 30% off code last month, but it was a one-time use code sent to my email that was linked to my Orbitz account (I was able to take advantage of it for our next trip and got an amazing deal!). I don't know how often they send big discount codes like that, but if you're not already registered with Orbitz it's worth a shot to sign up. I had an account with them and had booked with them earlier this year.