Ultimate Team Legends will be an exclusive addition to the Xbox versions of FIFA 15 (just like it was with FIFA 14). This has been revealed thanks to EA posting pictures of the covers of the different versions, with the Xbox editions carrying a sticker saying precisely this.
The Legends part of the game makes it possible to use the best players from football's history when you're playing Ultimate Team, and in the previous game you could choose amongst players like Dennis Bergkamp, Gary Lineker, Pelé, Ruud Gullit, Henrik Larsson and Patrick Vieira.