Agree with others that 15 pounds in a month would probably be tough. The fastest loss I ever achieved was right at the beginning, when I first started losing weight (I'm 5'7" and was 183 pounds at the time), and I lost about 10 pounds per month for the first two months. Generally, the heavier you are, the more weight you're able to take off per month when you first start out (all else being equal).

Keep in mind that you can't spot-reduce fat (that is, in order to lose stomach fat, you have to lose fat overall - there's no exercise or diet you can follow that will specifically make you lose fat in a certain area). The FAQ has a ton of info for getting started, but it can be a bit overwhelming, so I'll just break down for you what's worked for me. Check out MyFitnessPal - there's a smartphone app but it can also be used on your computer - when you first make an account, you input your height, starting weight, goal weight, activity level, etc etc and it will spit out a calorie goal. Track everything you consume, every day, and make sure you stay at or under that goal - and you will lose weight. That's really all there is to it. Weigh your food if possible (though I don't weigh my food and I've still done fine), but in general try to err on the side of caution by overestimating how much you're eating and underestimating how much you're burning through exercise. Keep in mind that weight loss is primarily about your diet - if you exercise, but overeat, you're going to have a much harder time. If you control your eating, you may not even have to exercise in order to see the pounds come off (though of course exercise has other health benefits, plus it's fun!)

Feel free to PM with any questions, and good luck :)