There's not much you can do with the last fifteen minutes of the day. You're about to face a traffic jam as you and a zillion other commuters all try to simultaneously occupy the same ramp to get onto the interstate.
It's too late to start a new project. On the other hand, you can't hang out at the water cooler for fifteen minutes, and you can't leave early. You can't take a break for the last fifteen minutes, because that's tantamount to leaving early.
Perhaps you should doodle. Or perhaps you should just start noding about your white collar ennui.