I have a slightly longer commute than that, although I only do it twice a week (I only work 3 days a week now, and one of those from home).
I leave shoes, shampoo & shower gel and a spare keyboard & mouse permanently in the office. My laptop & work clothes go in a 25L rucksack on my back.
My commute is just over 15 miles (25km) each way, and it usually takes between an hour and 65 minutes. Which means I'm riding a little faster than you, but not very much.
