I would guess it would depend on the date of purchase. If he found an authorized retailer that had an unsold 2015 MBP it might be possible since most warranties start on the date of first sale. OTOH, if it was an open box returned item, then the warranty would have long ago expired since it started on first sale. For example, I bought an open box iMac from Best Buy and it had 10 months left on the warranty since it was first sold 2 months before I bought it.
Correct, AC is based on original date of purchase, so you could certainly still add AppleCare to a mid-2015, as new ones are still floating around.