Eric linked the SXM restrictions. You also have to consider airline restrictions. 15 pounds is a little big, but I assume the dog will fit in a carrier under the seat? Because if not, then the dog would need to go in cargo, which I personally would not do for a vacation situation. Assuming the dog fits under the seat, they will need to buy a 'ticket' for the dog. Various airlines charge various fees for that, could be $100 or more, they need to check with the airline. Also, airlines have a limited number of animals they allow per flight, so if/when they decide they want to bring the animal, they should buy the dog's 'ticket' at the same time as theirs, to ensure no issues there.
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