We have 3 wins over P5 teams who finished with winning records. Out of 39 games against P5 teams. A 7.7% success rate. The number jumps to over 10% if you count a team that finished with a .500 record.
Our wins:
2018 Wisconsin (8-5)
2013 Texas (8-5)
2013 Georgia Tech (7-6)
2012 Georgia Tech (7-7)
Utah has 15 wins out of 82 games (18.3%).
Sounds about right. Utah has been about twice as successful as BYU since the split from the Mountain West.