I love the shot. Star trails are a cool thing that most everyone can do, and the results are quite impressive when done correctly. Personally, I'm itching to try it...but like so many have said, it's hard with all the light pollution...sometimes (rarely) living near the city sucks!
Either way, I'm curious about the post processing as well...sharpening, noise reduction...etc? Was it done in camera? I only ask because like exemplaria said, I've only ever seen trail shots done that were several exposures stacked together, not one 15 minute one. Not that it doesn't work, obviously, I've just seen a lot more done the other way.
But yeah, good job! Great shot, keep 'em coming!