Volume 15 is where the Blue Lock project moves from an internal experiment to a national spectacle. The tension is no longer just about staying in the program; it's about the very survival of Blue Lock against the established U-20 Japan team. Why "15" Matters

Across both mediums, "15" represents the moment where "playing safe" dies. Blue Lock, Volume 15 - Boston Public Library - OverDrive

The episode ends with the high-stakes choice of who to take for the next stage, a decision that shifts the entire dynamic of Isagi's team. Manga Volume 15: The Monster Ryusei Shidou