To walk a mile in 15 minutes, you will need to walk at a brisk walking speed of around 4 mph. Walking 4 mph on a level, firm surface equates to a MET score of 5.0 in the Compendium of Physical Activities. A MET score of 1 indicates the amount of energy used when someone is resting and sitting quietly. The MET score of 5.0 for walking at 4mph represents a moderate intensity activity.