Fitness fads come and go. Remember the Hula-Hoop workout? How about Jazzercise and pole dancing? But the latest trend — workouts that take mere minutes to complete — should have more staying power.

No time to exercise? Finding time to get fit may actually be as simple as changing your image of what a “workout” looks like. In fact, if you can spare 15 minutes, you’re on the way to getting the ...