So after you've cleaned something for 15 minutes then what? If it is something that really needs to get finished then take a 15 minute break (don't forget to set a timer) and then get back to it. Another alternative is to use this method to clean your house. Spend 15 minutes in each room, alternating rooms until all the rooms are clean.
Some advantages to this are that you don't get bogged down in your cleaning, it keeps you moving, and there is more motivation to finish quickly.