My commute is 24km each way (about 15 miles).
My house is 300metres above sea level so the ride down is much quicker, than the uphill climb home.
I don't commute every day, as I have two teenagers that have to be taken in to high school.
On days where I can work from home (like marking assignments) I take the boys in, leave the car and bike home, then bike back down to pick them up after school.
Some days my partner takes them to school and I bike to work. He leaves the car and goes for his ride, and I bring my bike and the boys home after work.
I think you'll find that commuting distances vary greatly with the girls here, and depend very much on things like the time of day and commuting terrain (I am lucky in that I have no interesctions/lights - I live in the country and my job is on the edge of town).
For example, when it is summer and I have no morning class, I take a rounabout route to work of 37km instead of the quickest way of 24km.
You are setting yourself very good steady and achievable goals. I really enjoy commuting