UN Convention Against Transnational Organized Crime
New Zealand is a party[1] to the UN Convention Against Transnational Organized Crime.
Under the terms of the treaty[2], I don't see why MEGA wouldn't be an "organized criminal group", and it would seem the US charges would qualify (more than 4 years).
[1] https://treaties.un.org/Pages/ViewDetails.aspx?src=TREATY&mtdsg_no=XVIII-12&chapter=18&lang=en
[2] http://www.un-documents.net/uncatoc.htm