What advantages do the 2015 13" & 15" MacBook Pro Retina's have over the new 2016, 2017, 2018, 2019 models?

You don't have to use adapters (Dongles),
USB 3 ports,
HDMI Ports,
Thunderbolt 2 ports 
No T2 Chip, 
Flash drive is removable and can be upgraded to 2TB, 
Wi-Fi card can be replaced if it's faulty, 
Reliable older style keyboard, (Not as noisy)
Smaller track pad,
Reliable Displays
Generally easier to repair.