I am still a seriously slow runner and I've been at it since January - I did 5.5 miles the last time out and averaged 16 mins per mile.
Some were faster, some were slower, but that was my average. I've been known to do a 10 minute mile, but I can't maintain that over long distance. I'm not too worried about it, I've been increasing the distance and not fighting on the speed as much. I ran 5 miles without a walk break this last time and was proud of that. Though, I have increased my average from 18 mins to 16 mins!
I walk to warm up and cool down, so that doesn't help the total time...
I didn't use the official C25K program, kind of made my own, but have heard great things about it. Just start slow, don't overdo too fast, and do what you enjoy!