I am 16, I weigh about 155, and have somewhat above-average breasts (36 D). I don’t find myself fat, but I think I could have a really nice hourglass figure if I lost about 10 pounds. Will this weight loss make my breasts much smaller? Also, will they lose their perk?

It will depend on the body type you have, well for some women while losing weight the size of their breast decrease, but you had mentioned you are 155 lbs and the size of your breast is average then I think it would not affect that much, check out this site for healthy dieting http://www.attractnaturalweightloss.com/