Bee,

If it is a 15 minute walk for you... why bike? When I had that short of a "commute", I walked and I would commend that to you. IMHO it would be a real hassle to bike that short of a distance and it would be an insignificant workout. OTOH, if you want to take a different route home for the purpose of exercising, biking to work could be just the thing for you.

Regards,

Tom
(Neophyte Bike Commuter)