15 Euro is the discounted price for the WAV files. The regular price is 20 Euro. I know PayPal is accepted, not sure about other payment options. It's a very small company, and website design isn't ideal at this point; however, I can tell you that customer service is excellent so if you email them questions you can expect a reasonably speedy reply.
PS. 15 Euro translates to $21.23 at today's exchange rate.