I'm sure it's either the Anker charging plug or the charging cable. I've got the exact same Anker charging plug and had the same issue, where it would take 90 mins or more to fast charge, where before the charge would take just over an hour.
I switched over to an older 30 Watt charging plug by a company called RAVPower, using the supplied Samsung cable, and guess what? I'm getting a full charge in 65-70 mins!