@dwayne33 As @george2001 said, the answer is yes. Here’s a little more info that may also help:
Depending on your account, when you checkout you may be taken to the address and shipping options screens before being taken to the payment selection page. On that page, under the list of credit/debit cards saved your account, you’ll see a checkbox that says “Your available balance: Use your $0.00 Gift card balance” (I don’t remember if you can enter a promotional balance or code here, but you could try). If you don’t want to use the credit, you uncheck the box/don’t enter any codes.
At the final checkout page, all accounts will have a payment method section on the left that allows you to deselect/change or apply any gift card balance on your account or add a promotion code.
Codes are not credits, meaning codes are not automatically applied to your account… you have to manually enter them. Since the $15 credit from this promo is issued in the form of a code, you should be able to apply it to any order at will (the code is restricted to items “sold by Amazon .com” or “sold by Amazon Digital Services LLC”). So yes, you’ll have the opportunity to apply codes during checkout and/or on the final payment screen.
Caveat: if you “click the button to add the coupon to your account,” you’ll no longer be able to enter the code so the $15 will be automatically applied to your order unless you deselect it on the payment and/or final checkout page as described above.
