Also 15mins is not enough time to perform a complete comprehensive training session including a dynamic warm-up some form of strength training followed by core focused work, cardiovascular activity, and a 5 to 10min cool down. The simple fact of the matter is that
for one to achieve their desired level of health or fitness they must make a commitment. Their workouts must be made a priority. I do this by blocking out an hour out of each day I am planning to workout for that week where nothing else is scheduled nor can be scheduled.
So remember if you only do 15mins it needs to be 15 intense minutes. Make workouts a priority plan and prepare for them.