I've done tons of research into buying an electric bicycle (pedal assist). From a spec point of view, this detail is easy to find but from a day-to-day user account, this is much harder to find. I'd love to know peoples' experiences with their daily e-bike commute. How far they go. Do they go further than they used to on a pedal bike? How long does it take? How tired do you feel after your commute? And quite importantly, which e-bike did you go for in the end and why?
I don't have an e-bike, but here's my view of them. The major problems that I see with e-bikes is that, in many jurisdictions, they limit the speed to a speed which is too slow. In my province it's 28 km/h. After you're going 28 km/h, the motor stops working. On a decent road bike, if you are physically fit, it doesn't take much effort to maintain 28 km/h anyway. I'm constantly passing people on e-bikes with my road/touring bike, and I'm not that fast.
So the electric bike won't help you get to your destination any faster, and may actually slow you down because of the extra weight added by the battery and motor. 15 miles is a little far for many people, especially for a commute ride. It will probably take an hour or more. If the distance is too long for you to pedal the whole way, you might want to look into other options for shortening your journey. Many cities have bikes racks on the bus that you can use. This would shorten the amount of riding you would have to do. I had a 25 km/15 mile commute for a while, and the only thing I didn't like about it was that it took too long. I was spending 2-2.5 hours a day just to get to work and back. But it took the same amount of time (+/- 10 minutes) whether I was riding my bike or getting a ride in a car from a co-worker.
I don't have an electric bike either. I do a commute of just under this distance each way every day and when used to it this distance is no issue. The problem I see with electric bikes is when resorting to pedalling only whether through desire or necessity you are "carrying" a hell of a lot of extra weight on top of the weight of the bike.
I totally agree with the suggestions made by Kibbee.