M.,
Have you tried walking? I have found that I lose the tummy fastest when I stick with my two mile a day walk. It only takes half an hour, and if you do it in the morning, before anyone else is up, it sets the tone for your whole day.
It is EXTREMELY difficult to make myself get up at 5:45 am - but it is SO worth it! You'll have energy all day, you'll feel much less stressed, and you'll just feel GOOD, because those endorphins (sp) have kicked in. Plus it's better for your metabolism if you do it in the morning. I also find I eat way less during the day when I've walked first thing in the morning.
If you've never been a walker, you probably will have to start with just a mile, and you may not be able to do it in 15 minutes, but it won't take you long to get to it. Also, with walking, you don't have to do it all at once. Maybe you want to do one mile in the morning and one in the evening....the benefits are the same.
Walking Magazine is great inspiration and has lots of great ideas (you can read it for free at the library, if you don't want to subscribe).
Hope you try it and it works for you. Blessings, J.