If you have a ShopSite Pro store, then you can set up a surcharge pull-down menu for Alaska and Hawaii. The feature is found under under Commerce Setup > Order System > Shopping cart. Help documentation can be found here:
http://www.shopsite.com/help/10.1/en-US ... harge.html
Another option, if you do not have a Pro store, would be to set up two more shipping options just for Alaska and Hawaii, and include the extra $15 in the cost. You can then change the text for the shipping options by going to Preferences > Store Text > Shipping.
-Nicole