That seems like a lot for shipping. Is that what the seller told you or are you using an eBay or Paypal(grrrr) driven postage calculator?
Maybe that is by registered because if it is small packet it should not be that much. Mind you....I have not sold on eBay for a while but I know that these calculators are way off sometimes and would think that regular mail would be less than $15.
This is one of the reasons I don't even bother with eBay anymore since Paypal dictates how much postage should be.