14 hours a week is 2.8 hours a day (ignoring weekends) on top of classes you spend in school. We had at least 4 hours a day of lectures during first year. That amounts to 6.8 hours a day not counting countless hours during exams time. It is not that little given that most people are unable to focus fully without breaks, so they have to happen too. In addition, you do count unproductive time in work (pointless meeting, small talk with colleague) as a work time.

Most people can learn only so much withing a day and can focus only for so long. I would guess that 6.8 hours can be quite close to the point where your focus run out and you are bound to waste the additional time by staring on book (as opposed to learn from it).