I want to enjoy watching a pedo getting his shit pushed in. But with these vigilante people/groups you have no idea what standard they are using.
Right off the bat, I expect to see evidence from the dating chat showing that he knew she was 15. I have not seen that.
Pretty much every dating website has a minimum age of the legal dating age in the country. I would assume 18 would be the minimum age in the US. Anyone younger is breaking the terms and conditions. Most people would presume that they are chatting to legal adults on a dating website. If not, that person lied about their age just to get on.