For years the AFC South has been a low-threat division and the 2015 season was no different in this regard. Much of the imbalance of the South has to do with the division's lack of quality at the quarterback position. Only the Colts have a reliable answer under center. The Jaguars aren't sure what they have in Blake Bortles (regardless of what their ownership and staff say). He was woeful often last season, and never displayed the poise that was promised in preseason tilts. He also doesn't have a proven corps of skill players around him, along with a poor offensive line.
The Texans failed yet again to answer their burning question at QB. Since this isn't the year 2000, its going to be near impossible to win against higher caliber opponents with such a lack of quality at quarterback. Convincing yourself that Brian Hoyer is a starting caliber player won't get you playoff wins.
The Titans don't know what they have in Mariota yet, regardless of the hype. But expectations are high, and the ex-Duck comes into the NFL with a trail of impressive college tape (and records to boot). If he can grow into the passer he is expected to be, the Titans can elevate their position in the division, and challenge the Colts for a spot at the top, even if that year isn't in 2015.