The really crappy part is how much of that 15 miles is caused by car infrastructure. Imagine how much closer one might be to work if the distance were compressed, removing about 80% of all street and highway width, the entirety of all road buffer zones (highways often have several times as much of this as they have actual road), front yards (= mostly to keep house back from busy road and allow space for cars on driveway), parking lots (often several times as large as the place they're meant to serve), and so on. I'd be surprised if such compression didn't shave about half the distance off.