2015 was when official rules were put into place to protect Net Neutrality. But before that, ISPs had generally worked in a way favorable towards Net Neutrality

2015 was when official rules were put into place to protect Net Neutrality. But before that, ISPs had generally worked in a way favorable towards Net Neutrality. But then they started to act against Net Neutrality and then the rules were put into place. So, you could argue that we've have net neutrality in principle since the internet existed (or at least up until 10 or so years ago when ISPs started to push back) but we have only had Net Neutrality enshrined in regulation for a couple years. It appears that going forward we will have neither.