At 15, it's natural to want to see sexually explicit material. However, there are some reasons that your developing sexuality might be negatively impacted by watching porn. Here are some potential reasons:
1. If you are watching porn that is violent or demeaning to men or women, you can teach your mind to link sex and violence or sex and degradation. Have you taken Psych 101 in school? Humans can be conditioned just like Pavlov's dogs. We link two things together long enough and they become linked in our minds. And when that happens, it will affect your sexual triggers and may negatively impact future relationships with real women.
How to combat that: Well, first, you could watch porn that is not demeaning or violent. "Demeaning" is a subjective term, but generally, it means that the porn would include actual violence or degrading language such as name calling, rape scenes, etc. So be careful what you decide to turn on to because it could stick with you life long, and impede your sexual relationships with healthy women.
2. Many young people, and even some older people, think fiction is reality. Porn is fiction and does not in any way depict how real adults have sex. Even "good" porn is still fiction. Do NOT expect your sexual encounters to look ANYTHING like what you see in porn. It will cause you to really have disappointing experiences and relationships if you expect that.
How to deal with that: Tell yourself often that this is fiction and it's not how sex works. Make sure you have fantasies about REAL women or men in real situations. People don't, in reality, have one drink in a bar with a stranger and then go have a threesome. Women don't pick a guy up on a roadside and have sex with him in the car. People don't pop out of a closet and join an orgy. Keep your brain real.
3. Real bodies don't look like porn bodies. Now, the folks who act in porns are real people of course, but it's their job to cosmetically change themselves to fit a very narrow and unsustainable (and frankly, not actually pretty when you look at it with fresh eyes) paradigm. Women in particular don't look like that in person. The people in porns have often had much cosmetic surgery, been airbrushed, and work out for hours a day to maintain the body types you see in mainstream porn, like Vivid and those companies. The women often have surgery on their genitals to make them look unnaturally small and childlike. So training yourself to turn on to a "porn look" is also really going to lead to disappointment and lead you to potentially unnecessarily judge women by a standard that is likely to result in loneliness for you, because we just don't freaking look like that.
How to deal with that: When you are ready, get with real women or/and men and see them as beautifully unique. Don't judge by porn standards cuz they aren't real.
4. Watching porn too much, or doing anything too much, keeps you from living life. You are 15, so you need to be out in the world having fun, studying, seeing movies with friends, roller blading, camping, and eating pizza. Don't let porn become too big for your life, or it will deprive you of social experiences and this WILL negatively impact you.
How to deal with that: Give yourself time limits and stick to them.
5. People who watch porn often get the idea that women and men in porn are "different" than "regular people," and while they may be cosmetically enhanced, they are not different beyond that. Sexy women and men are not to be looked down upon, disrespected, or called "sluts" and things like that. Porn tends to use demeaning words and that's wrong. A woman who has a lot of sex is NOT less valuable in any way than a woman who makes more conservative choices. Judging people for sexual choices is evidence of a small mind. Do be that guy.
How to deal with this: Recognize that penises don't take a piece of a woman's worth with them when they leave. Don't call people negative names for their sexual choices, regardless of what they are, including calling women who are virgins "prudes" or "frigid." Negative judgment for life choices is not what decent people do to one another.
I'm a mom and a former men's magazine model (never did porn, but some of my friends back then did)