Net neutrality wasn't instituted in 2015. It was made law in 2015. Prior to that, Net Neutrality was the standard since it was classified as an information service. It wasn't until telecom companies started blocking VoIP traffic that it changed.
Net neutrality has never been made law, as the 2015 FCC Open Internet Order is not a law. The FCC cannot write laws. Full net neutrality, as defined here [1], has also never been mandated in the US.
The 2015 Open Internet Order mandated "net neutrality protections", not net neutrality itself.
