The original Chromecast was released on 24th July 2013 and has since sold over 20 million units. 2 years later, Google finally unveiled an updated Chromecast and announced it during a special event that was held on 29th September 2015.
You can call it Chromecast 2 or Chromecast (2015). I would prefer Chromecast (2015) since the product name is still called Chromecast and Google uses the slug “chromecast_2015” in its store URL to buy the Chromecast.