Well I'm glad that he told you.
I wish I had taken the same action as him.
Since I was 13 years old I was attracted to kids my age and younger boys.
I knew I was gay, but as I got older and older and still felt an attraction to younger kids I saw that it was a problem, but I never told anyone about it because of the fear of being rejected and the way people think about you scared me so I held my biggest depression secret. When I was 13 years old I found a lot of images of child sexual abuse. I download some that I wish I had never watched. I kept watching and downloading until I was 21 years old when the FBI finally got me. This can sound bad, but it was such a relief for me to get caught so I could get help, because there is no help everybody that feels the same way I felt needs to be caught to finally get help and that is sad because most people go to jail first. I know people that went to jail because they download child pornography but never abused a child, which is the same situation as mine. I never went to jail that's because the FBI still working in my "case". I'm scared and every person that I know from my group therapy was scared of going to jail. I don't know how people feel about people like me, but going to a prison sounds horrible because you never got help to cure myself of this problem that you don't know how to solve. Then you need to go to jail and be there with people that are worse then you, not judging because everybody has their problems, but it is scary to be there with murders.
So I live in the US but I'm not from the US either. I'm really glad that your son told you about what he feels. A lot of people don't tell their parents because they feel like me and all the other people that couldn't tell with the fear of being interpreted wrong because let's face it the world interprets wrong. They don't care about you; they want you to die or go to jail.
He is 15 so is still a good time to find a therapist to help him. Look for a therapist that works with sexual offenders (that's what they call me but I hate this word). Why? Well no one helped me to fix my problem, then they call you that and put you in jail and the worst part is with your label I'll always be dirty.
Not calling your son a sexual offender, he isn't one just like me. Why find a therapist that works with sexual offenders? Because they will not judge your son like some other therapists do because they don't have experience with this type of subject.
I'm 22 years old now and if I was your son's age and my mom knew about my problem I would like my mom to be open and understand what I feel. I don't know how to fix it, but I'm willing to try really hard to change. (By the way now my mom knows and my step dad and my sister also know; they have really been a support in my life.) So just be patient with him, don't judge, and remember that he told you something that is really hard to tell anyone.
Make sure that he is not downloading child pornography / accessing any place that he can get images / videos of children in the age that he has an attraction to. Child pornography will not help. It will just make the feeling worse and if you want to change you have to commit yourself to not go to the place where it is slippery.
Some things that you need to know of:
Depression / no friends / fear to go to places like shopping malls / thinking of suicide. That is what I felt most of my life when I was 13 to 18 years old.
Depression: staying at home a lot eating, playing video games, surfing the web, not doing exercises, missing school. Not going to places where you can see another kids in both young and older ages.
Suicide all the time, I never tried to kill myself, but I always though that the world would be better if I killed myself. Or why god choose me to be like this and not someone else. Some suicidal thoughts that I had like buying a gun and shooting my head, freezing to death, taking some medicine like a lot until I overdosed, or asking a friend to shoot me in the head. I never used drugs and I don't drink, but I though of using drugs until I die or don't feel in my normal state of mind anymore, drown myself.
So be aware of that and help him out, just make sure that you are open to help him because this path is not easy but he still young so maybe tell him some stuff that I talked about here, so he can be aware of it too.
Some people are recommending forums. I do not recommend any of them. From my own experience, in some of these forums there is a lot of people there that they don't want to change. Some people may try to manipulate you to do bad things and don't let your son join any of this forums. If it is for yourself so you can find a better way to help him it's fine, but if it is for him to join, just don't. There are a lot of people in these forum that are willing to help you, but there are a lot that just wants to do bad things.
Even though your son feels attracted to young kids a forum like that can be a way of other people trying to manipulate your son. So just be careful.
Virped, I do not recommend. A lot of people there don't want to change (I tried to get help at this place and they banned me saying that I couldn't change) and let's face it, the one with the name virped was really rude to you.
After 2 hours I was able to find an article that I read a while ago about a 19 year old pedophile, and I feel exactly like him
It's an audio on sound cloud:
https://soundcloud.com/this-american-life/522-tarred-and-feathered-act-two-help-wanted < listen to this audio.
If you have any questions let me know. I'm glad to help people in the same situation and I hope some day we will have a better way to be helped without going trough the system.