My commute is about 15 miles each way as well. I shower in the morning and then bird bath at work. One of the things I always do with work or school is scope out the bathrooms. Which ones are high traffice etc. Anywho, we've got 2 small bathrooms with locking doors that I use. I dump water over the head to help remove sweat and helmet hair. I've got longish hair and I don't care if I look like I just stepped out of the shower. When I bike in, I'm usually an and a half early as to avoid people anyway. I'm going to propose that a small shower stall go in one of the bathrooms.