http://www.fbschedules.com/ncaa/sec/tennessee-volunteers.php
According to this site, Tennessee has four non-conference games for next year. They host Oklahoma, so playing Baylor would give them two tough non-conference games next year.
They start the season playing Bowling Green in Nashville. They were supposed to play UAB then but they dropped their program. Tennessee already has four games scheduled for 2016, with Virginia Tech at Bristol being their toughie.
They only have three games in 2017, with none of them being from a power league. They have West virginia (and no one else yet) in Charlotte in 2018 and Southern Cal home and home in 2021/22.
Baylor is at SMU next year and has them at home in 2016. Their next open spot is in 2018, with nothing open in 2019. They play at Duke in 2018 as their only game against someone from one of the power conferences.
My guess is Baylor called Tennessee when UAB dropped football and tried to get a game. If they wanted a home/home with Tennessee, I doubt Tennessee wanted to play their home game with them in Nashville. I would imagine backing out of their contract with Nashville would cost them a bundle.
So unless Tennessee wanted to play two tough non-conference games in one season, they could not play them any earlier than 2017 with a rematch in 2019.