Time is a rare and valuable commodity in most of our lives. There's never enough of it. I am constantly learning how to better manage my time, how to serve better with it, how to be a better steward of it, and how to make every minute I have count for as much as it can (on both an esoteric level and a very practical level).
15 minutes isn't a huge amount of time, but with it, I can fit in anywhere between 15 and 40 pages of reading a day, allowing me to consistently move through quite a few books at a reasonable pace. This concept of using a small, dedicated period of time could be applied to a number of different activities.