The fifteenth card in all Dragon's Maze packs isn't basic land; it's nonbasic land. All ten guildgates will be showing up (with the Dragon's Maze expansion symbol), as will all ten shocklands from Return to Ravnica and Gatecrash (with their Return to Ravnica or Gatecrash symbols). You are about half as likely to open a shockland in Dragon's Maze as in Return to Ravnica and Gatecrash and, since this is for all ten shocklands rather than five, that means you are about a quarter as likely to open a specific one. There's also a mythic rare land from Dragon's Maze.