Hello! We've never offered the game for sale here at that price point. For a limited time I offered it at $5 USD during a sales bundle event that was for a specific build and labelled as such, both at the button and in the game  description as well. This was a test as an alternative to Patreon but it ended up being confusing, so we stopped offering it. I don't know where you got the 15 USD price from, but I am happy to offer a refund if this was a misunderstanding.