Will my sag if I lose 10-15 lbs?

I am in my mid 20's and need to lose about 10-15 lbs but I am sooo scared my will be saggy! I don't have the perkiest s because I am a D cup, and I am an average women. meaning, we don't all look like the girls on TV. So, i really want to get in shape and feel "y" but I don't want to have s that look like i've hasd two kids when i haven't. Since im younger and only have 15 pounds to drop am i more likely to just have my get smaller without the sagging? Thanks!