Are you eating enough? The bare minimum a woman should eat is 1200, if you workout hard, you will need more calories. Some women, even when eating 1200-1400 calories still enter starvation mode, so their body stores additional food as fat.
Have you done an online BMR and calculated what you should be eating from weight loss from that?
http://www.bmi-calculator.net/bmr-calculator/harris-benedict-equation/
When I first started losing weight, I ate 1300 calories a day and didn't lose anything, in fact, I gained 8 pounds since I wasn't eating enough. It's strange.
When I upped my eating to 1600, I lost 2lbs every week.
15 pounds is quite a lot to gain in 2 months, however, if you are noticing your clothes are feeling looser, then you will be turning fat into muscle, muscle is denser.
If your clothes are getting tight, you need to re-evaluate your eating and exercising.