Despite hoopla over details...despite your disclaimer of genral poll.....(.and I am guilty in earlier reply ) I like roadbikes in general for commuting use.

I use my Japanese 8-spd (looks like a english 3 spd.) for my 11-12 mile round trip commute. This one is currently outfitted full fenders rack etc.

For longer commutes, especially if wind is involved I prefer having drop bars. Currentl;y my drop bar bike does not have fendes/racks.....but it did when I was using it for commuting.

both are posted on the 20 year old clunker thread if you want to take a look

but in general for 15 mile round trip I think you have a lot of flexiibiliyt.....longer warrants more efficiency