I also suggest you stop smoking and do not diet. Take proper nutrient food like leafy green vegetables, fish, grains, fruits and eggs etc.
Do exercise as well.
Agree with ScalpMassager, all the way. The most important thing you can do is stop smoking, and you don't need to lose weight. I know that's probably not what you wanted to hear, but dang, isn't that how it always goes, when you ask adults for advice?
Gender?
Smoking will help you not grow taller (making you appear fatter for the same weight). Without smoking you might have the potential to easily grow another four or five inches, maybe more and become svelte and slim.
At 110-115 lbs, you're at a good weight for your height. Just maybe 5 lbs generous but you're only 15, it's important to allow for grow spurts so that the most can made out of them. If you lost 15 lbs, you'd slip into the underweight (heading towards anorexic) BMI category (which does not really apply to children but pretty close for your age). You can expect side effects (more likely to have blemishes for example imo) And, you would again likely impede your expected continuing growth in height.