15%+ is fine afaik and I think even 12+ is fine for most ppl (don't quote me lol, i'm a guy).  The $5 calipers and a body tape measure is really all you need, it will give you a relatively accurate and more importantly consistent measure of body fat all over (there are several points you measure from).  In a relatively fit person (normal range above) exercise has a big impact on body shape/overall appearance, moderate cardio is where its at for ladies :)