You already have a great plan right there. Aiming for a higher goal every day really helps to see if you can push yourself to that next level. 15 minutes is great if you are just starting out. You can build up along the way as your body gets used to the new change and you start putting on muscle. At least you are exercising and doing something, it's a lot better than doing nothing and crashing on the couch in front of the tv every day
