From https://support.apple.com/en-ca/HT201736 we know that he does not have Thunderbolt 3.   MacBook Pro from 2016 and later has two Thunderbolt 3 (USB-C) ports on each side   From his post we know he has TWO Thunderbolt 2 ports.   MacBook Pro (Retina, 15-inch, Mid 2015) has power, two Thunderbolt 2, USB-A, and Audio-out on the left side   Each Thunderbolt 2 port is 20 gbits which is exactly what is needed for 4K that is limited to 60 hz   He nee