Some US states are 16 as well, others are 16 with age restrictions on the other partner (under 20 is an example). I remember it coming up during Queer as Folk, but it came out that Pennsylvania (where it was set, though filmed in Toronto) had 16 as an age of consent.
That said, I also believe they should throw the book at this guy. A 15 year old lacks the ability to make decisions in this manner, and the guy took advantage of that as well as involved himself in child pornography. This is different than engaging in "don't ask, don't tell" sex as an adult or not knowing one's status.
As far as when one becomes an adult, our founding fathers probably had it right when they put the legal age of majority at 21. Human development studies show the brain isn't fully mature until about 25 (as is the body), and while one learns from making decisions and even mistakes, a person also needs to be protected from the potential risks and harm caused by certain decisions.