The fifth generation of Pokémon began on September 18, 2010, with the release of Pokémon Black and White in Japan for Nintendo DS. The games were originally announced by the Pokémon Company on January 29, 2010, with a tentative release later that year. The final release date of September 18 was announced on June 27, 2010. This version is set in the , inspired by New York City, and utilizes the Nintendo DSs 3D rendering capabilities to a greater extent than Platinum, HeartGold, and SoulSilver. A total of 156 new Pokémon were introduced, starting with Victini and ending with Genesect, bringing the franchises total to 649. This is the only time that the number of Pokémon introduced surpasses the number introduced in the first generation. It also deployed new game mechanics such as the  wireless interactivity features and the ability to upload game data to the Internet and to the players own computer. Pokémon Black and White was released in Europe on March 4, 2011, in North America on March 6, 2011, and in Australia on March 10, 2011. On June 23, 2012, Nintendo released Pokémon Black 2 and White 2 in Japan for Nintendo DS, with early October releases in North America and Europe. Black 2 and White 2 are sequels to Black and White, with several events in the second games referencing events in the first; they also allow players to link their previous Black or White with their Black 2 or White 2, introducing several events based on how they played their previous game.
Question: How many months after Pokémon Black and White was released did Nintendo release Pokémon Black 2 and White 2 in Japan for Nintendo DS
Answer: 15