1500 calories could be a bit much, also, what kind of exercises are you doing? Our bodies often Plateau and need change. It's very important to change up your nutrition as well as your exercise routine at least once a month is what I would recommend. Don't let your body get use to a routine or a specific nutrition plan. Changes confuse and shock your body into burning calories more efficiently. If all you're doing is cardio, I recommend changing it up to some type of weight lift or bodyweight interval training.
Sometimes your body can hit a wall causing your body to burn fat at a slower rate I hope this helps.
It's possible that 1500 calories is too much for your body, or that you aren't eating the right kind of calories.
You might also want to have some simple blood tests done to rule out a thyroid condition, called hypothyroidism (under active thyroid), which makes weight gain difficult to impossible. The tests you need are TSH, Free T3 and Free T4.