Sounds like they're fishing. They're seeking a low-wage master w/15 years, yet they're willing to talk to a relative neophyte such as yourself? (No offense, of course!) While in this economic environment anything is possible, odds are good that competent 15+ year folks are running their own companies, or otherwise engaged. Remember, 15 years ago, Windows 95 was new, and about half of the common programming languages used today were barely newborns. Not that that matters much, depending on the position, but if you're really outside of their target, they wouldn't have wasted the phone call. (Generally speaking...some HR folks are bizarrely thorough.)
From the interview results, sounds like they're looking for someone who has a certain level of determination, who can finish the job. Probably not a 'cocky know-it-all', but someone who will work for a smaller premium, and do 'janitorial work' that's cost-ineffective for their 'stars' to do.
On a side note, sometimes being nervous during the interview is a plus, simply because it shows you actually care...a rare quality these days. Too many applicants are so arrogant and/or their resumes are so padded, that sometimes it's refreshing to come across someone who's more or less honest about their abilities...and lack of same. Lack of confidence is not even close to the same as lack of competence, even to the die-hard HR pinheads. As time passes, you'll not only slip into your role in the company, but occasionally, a lack of expectations can lead to positive surprises.
Oh, and the really annoying factor? Bosses tend to prefer to hire folks under their own skill level...because they won't be a threat to said boss' employment. So sandbagging can be a quite effective career strategy, if you play your hand with a bit of skill.
I.e., never feel guilty about being the low person on the totem pole...you should always aim to be in the company of giants. At the very least, you can learn far more from your peers than you'll ever learn in college.
Happy Hunting!