Are these Dresses are to Slutty for a 16 y/o...My Mom thinks so :S?

Not at all!! Many people from my school banquet wore dresses very similar to those, and people were told to wear formal attire (or semi-formal attire at least). I wouldn't wear those to the mall or school exactly though. They're not too casual for that type of setting, and I'm sure you'd get in trouble for wearing too revealing clothes (at least in my school we would).