Welcome to TE and the wonderful world of bicycle commuting. I commute to work 16 miles each way. I had a Trek steel touring bike, but sold it for a cyclocross bike to commute on and hopefully do some CX races next Fall.
I have a mountain bike also, but since my commute is pretty long, I opted for a road style bicycle for the job. The drop bars offer more hand positions and it is faster than my mountain bike.
I was nervous about getting a road bike also and wasn't sure if I would like the riding position. I opted for a relaxed geometry Bianchi via Nirone road bike and absolutely love it. It didn't take long to get used to the different roadie position either. The key is to find a good fitting bike for your body. The only way is to test ride lots and see what feels best for you. Lots of threads on this if you decide to do a search. I would say go for a road bike if that is what you want, or at least try a few out to see if it works for you.