Tempting, yes, however, compared to the interest rate the credit card charges (usually MORE than 15%), they will receive MORE in interest charges than the 15% off they advertise. It is not worth it to charge items on a card that has a percentage MORE than the DISCOUNT!
Usually they will offer the extra 15% off so new customers will be "drawn in" and apply for the new credit card. They instantly get the 15% off their purchase. DRAW NEW CUSTOMERS would be my answer.
May 5th, 2015
I worked for Sears for a few months and we used that ploy on customers who didn't have the Sears card already. They got 15% their immediate sales, not knowing how much the interest rate would cost them.