The more workouts you do, even if they are only for 15 minutes, will help your muscles to get out of their comfortable zone, and get a bit stronger every day !!
See, i keep my exercise ball , and work out my core a lot for strengthening , and it does make me feel more in control and fit . I think everyone should get one of these. Mine was given to me by someone special and so I have two reasons on why to use it. My core and special one.