For context, 15 was some brony tf2 player who cracked deep voice synthesis in order to make My Little Pony characters say funny things. He then offered this for free on his site. It was never a clever branding thing, it was just his username.

It's funny seeing HN types being genuinely confused as to why someone would just make interesting things for the sake of making them, and then offer them freely for the good of others. He used to be on HN, there's good insights in his posts: https://news.ycombinator.com/user?id=15ai