The official Pokémon Tretta website has announced the 16th set for the series.
Pokémon Tretta Ultimate Set 2: Glaciate! Kyurem's Assault (ポケモントレッタ アルティメット2弾 こごえるせかい! キュレム強襲) will be available starting May 14th, 2015. The set will feature the first ever Ultimate Class Tretta for Kyurem and first ever Master Class Tretta for Ho-oh.
Preliminary details have been added to our Tretta page and will be updated when information is announced.
Source:
http://www.pokemontretta.com/tretta/t16/index.html