No college team has yet gone 15-0, and I don't think any college team has won 15 games in a season at all. So 14 wins is the high point so far in college football history, and only a few teams have done that. If I'm not mistaken, BYU went 14-1 back in 1996. They played in the Pigskin Classic against Texas A&M, which back then was an extra game (Kickoff Classic was the other such game. You may remember we beat Ohio State in this game to start the 1986 season. Pigskin Classic was played on campus, Kickoff Classic was played at Giants Stadium at the Meadowlands). They played what was an exempt game at Hawaii, the new WAC championship game, and the Cotton Bowl game vs. Kansas State.
I believe we were then the first team to go 14-0 in 2009***. Schedules had expanded to 12 regular season games, the SEC title game, and then the NC game vs. Texas. I know Ohio State has gone 14-1, and Clemson has gone 14-1. So, I think BYU, Alabama, Ohio State, and Clemson have been the only teams in college football history to win 14 games in one season.
The point of all this rambling is that Nick Saban has done this three times at Alabama.
***I went back and looked an Ohio State was actually the first 14-0 team in 2002. A quirk in the calendar allowed an extra weekend, so teams played 12 regular season games that year. They were still doing the preseason games and Ohio State played Texas Tech in one of them, which made 13 games, and then the Fiesta Bowl NC game vs. Miami.