Maybe talk to him about the problem? I'm a 15-yr-old boy and my parents trust me completely.
If you try to block him from stuff, it just has an effect where he will try even harder to get to what you don't want him to see. trust me, it'll be a negative effect in the long run.
Hope I helped.
I'm 15 too and feel exactly the same way.
I know people and have friends who aren't allowed to drink because their parents said no, so they go out and get completely plastered behind their parent's backs. It's becoming a very serious problem in England.
Most of the parents are all "We don't want them making the same mistakes we made when we were young" so the kids deliberately do that sort of stuff.
Myself? I am allowed to drink in moderation. My parents even encourage me to drink at times and buy me alcohol every 6 months or so... and thus I don't go out and get so drunk I can barely walk - trust me, I've seen it to happen to people my age and younger. It's an appalling and pathetic sight.
If your kid is watching porn, let him. He'll do it more if you tell him not to. It's how kids work. I'm sure you must remember when you wanted to do the complete opposite of what your parents said - standing up to the oppressors and all that.
At least he has a healthy interest in sex, on the positive side. If he didn't, you should be worried about your teenage son. In this day in age, it's almost impossible to keep kids away from sex. It's on TV. It's in films. It's on the internet. He's going to be interested in it for some reason. Even if you isolated him from those things, his friends would still talk to him about it.
However, there really isn't much you can do when it comes to filtering the Touch. I'm guessing you'll just have to trust him not to go on porn - and if he does then let him. At the end of the day, it's unlikely to do any serious harm to him. Either that or take away his iPod touch... but in the long run, that's likely to so more damage. Conflict at home, etc.
I'm also a father of two, and I don't mean to rag on the OP, but can someone please explain to me why a 15 year old needs an iPod Touch in the first place?
I'm 15 and I want an iPod touch really badly.
Reasons I want one:
-It's an iPod. I love music, as do most teenagers, and I want to listen to it on the go
-It plays videos. I love watching videos and would like to watch them on the bus to school.
-It has wifi. My entire life revolves around the internet, I want to take it wherever I go
-I love Macs. It is technically a Mac since it runs OS X.
-Can't afford an iPhone (darn tariffs) but love the UI. Self explanatory.
-It's cool. Again, self explanatory.
lol so yeah, I take it that those are probably the reasons why a 15 year old would want an iPod Touch. No-one NEEDS an iPod touch. No-one NEEDS and iPod. It's just about what we want. For some, they want a Nano. Others want a Classic. And so forth. You make it sound like you've got to be a sensible adult to enjoy these things. Really, if you can afford it, buy it

I spent 9 months saving up for my iMac by building, cleaning and selling my old Lego sets on ebay (I was 14 at the time). I don't see why I shouldn't have on just because I'm 15

and I probably need it more than a lot of people who buy iMacs.