I also have a 15 mile one way commute, over rolling hills.
I ride a bike which is built on a touring bike frame. I have fenders, generator powered lights, rack etc. The bike, when loaded weighs more than 20lbs, but it is pretty quick. I make my commute in about an hour without really pushing it.
In your shoes, bikes that I would be looking at would be things like the Surly LHT, and the Trek 520 (do they still make those). Drop bars put you in a lower position which will help your speed.
I carry my clothes, lunch etc in a pannier. When I am bringing work to/from the office, I use an arkel briefcase to carry the laptop and paperwork.