1500 calories doesnt sound like a very good number. Try googling a daily calorie intake calculator. Awhile back I calculated mine, and it said that I needed to consume around 1700 just to maintain my weight. If I go over that number, then I'll gain... but if I stay under that number, I'll loose weight. I'm probably a little heavier than you, so I wouldnt go by mine. Lol.

It just really depends on your weight. From what I remember, I think for every pound you want to lose, you need to take away 500 calories per day. Just dont go too low, because if you do your body will go into some kind of starvation mode and freak out... and store fat. So you could be eating 500 calories, and lose weight for a little while, but then you'll come to a dead stop. That was my problem. I usually try to stay around 1000, and it seems to be working.
I would assume a calculator would be most accurate, next to seeing a doctor.