get it now. where you set a certain amount and the person can click the get it now and automatically spend those credits and be the winner. Im not sure if you are too new to be able to do it. i dont remember how long you have to be on to be able to. A lot of people will offer a gin (get it now) and offer to ship for free if you use the gin. A lot of people just dont bid on stuff where shipping is charged so this works out great for both parties.
Your new so you prob can't do GIN. You need your sellers wings
$15 is a lot for shipping, if you put these in a medium flat rate box or plain box you can shop for cheaper. People are drawn to auctions that have free shipping or low shipping costs, so say if you charged 1/2 of the $15 - ($7.50), people might be more apt to bid and pay.
Unfortunately you will encounter the few who will, bid, win and claim they didn't see shipping and refuse to pay the costs, or reverse to pay cause shipping is to high, or they don't have the $ to pay... Just beware of the few pains in the rear, but over all the majority Listians are awesome.
Welcome to Listia, if you have questions don't be afraid to ask!! We will all help out :)
You should add an update that if credits go over a certain amount you'll offer free shipping :) I do that and it works sometimes. Entices the bidder :) good luck and welcome again to Listia