Barely out of puberty and already a medical expert. Tobacco products have a cumulative negative effect, at 15 yo it's unlikely to show signs of wear and tear on ones body. Hasn't your dentist told you smoking is one of the leading causes of heart attacks? Hasn't he told you smoking creates plaque that leads to gum disease? I'd be in the market for a new dentist.
Being a smoker myself I can tell you it takes it toll after many years. Lungs may be fine now, but many smokers have COPD, like me, gum disease like me and have spent 20k so far on bone graffs, sinus lifts, implants and I'm not done yet. This ordeal is now going on 2 years of discomfort and major expense. This is just tip the iceberg of the medical problems than can occur from tobacco.
Not only are these products very costly on a day to day basis, but premiums are much higher( if they write you at all) for life insurance and healthcare.
I know people have gr parents that smoked for 75 years and lived to 90.........those are just a few of the lucky ones,many aren't that fortunate. To paraphrase something Roadwarrior said a few weeks ago, "don't take this kid's advice".