This version of Doraemon for the NES is a hacked ROM, modified from the original Japanese release by Neokid. This 'Mapper 15 Hack' likely refers to changes made to the game's internal structure, potentially altering gameplay mechanics or adding new features. The English translation by Neokid v1.1 makes the game accessible to a wider audience than the original Japanese version, which further demonstrates the enduring popularity of Doraemon globally. The hacking community's efforts allow for expanded access and enjoyment of retro games.