I have one Visa (via my Credit Union) and one Master card. The Master card is a "back-up" in case the Visa can't be used for some reason. On the Visa, I get "brownie points" worth almost 1% of what I spend exchangeable for merchandise or airline tickets. I never carry a month to month balance and pay on line with a (free) funds transfer. The Visa credit card is the payment method of choice for me. It works for me.

I would hate to keep track of 15 credit cards. :)