Colts did have a young elite QB still in 2015. Brees was 36 vs. Luck turning 26 at the time so I can see why Payton to the Colts could’ve happened. Brees still had 4 years left of top 5 QB play though plus a playoff team around him so the Colts situation wasn’t strong enough to leave.
The Chargers are the 2015 Colts with having a young franchise QB and possible vacancy. But Staley is in Payton’s way of his dream location. It’s unlikely that he’ll drop those last 3 games to 3 win/4 win teams so his job can be handed to Payton.