That's not $15 million

Mason tells Tyler that the key leads to a bank safe deposit box where $15 million is stashed. At the end of the movie Tyler disguises himself and goes in to retrieve it. He grabs one small bag and hustles out.

Now, I'm no expert on such things but I've seen displays of large sums of money in other movies and TV shows. There's no way $1 million would have fit into that bag and safe box, let alone $15 million.