True but 15 million is still 15 million. I definitely wouldn't advise him to turn it or any first round money down in a risk to get more a year later. Even if he's a bust and doesn't see a second contract that kind of money can feed a family for life and, if played and managed right, feed the next several generations. If you have a first round draft grade, unless your family is already completely financially stable, you need to go get that money.
Like someone said earlier in the thread, any team talking down on Tua is simply hopelessly trying to get him for cheap in his first contract. There is absolutely no way he falls out of the first round. I would be absolutely shocked if he wasn't one of the first 10 picks, unless his recovery outlook takes a huge nosedive between and April.
Selfishly I would love for Tua to return but he should go. He's already a BAMA legend, a CFB legend even. Screw a Heisman and records and a possible additional ring. Go get that money.