16 miles is completely do-able. I went from 6 miles for a few weeks (to get into cycling - prior to this I had done NO cycling for years!) then to 11 miles each way for 6 months. I have done barely any cycling since finishing uni and am going back to 11 miles each way 5 days a week in feb. Once you get it done a few times you won't even notice it.

I have set my personal maximum for a commute at 20 miles each way.