A grande latte on a Royal Caribbean ship the last time I was on it was $4.50 plus 18% gratuity. Two punches comes to $4.87 with the gratuity added. You come out ahead if you use all 15 punches, by $3.82. Due to the fact that there is an odd number of punches there is a chance you leave a punch behind, further diminishing the value.
Go ahead and buy the card but to suggest it is a "no brainer" means you don't know much about the card and don't have much in the way of experience with Royal Caribbean.
But please continue to post screen shots, they're entertaining.