Mine is 12 which usually takes 45 minutes with morning traffic. I wouldn't mind a few more miles, but anything that takes more than an hour is a little excessive. Anything under 30 minutes is not enough time to even get sweaty!
Also, 18mph average is pretty quick if you're going to be on urban roads. Be careful not to go so fast that you can't brake in time for common cyclist/motorist accident situations: right hook, left cross, parking lotted, etc etc