I believe BYU has 15 P5 wins since independence. That's more than Boise and any other non-P5, although we easily have had more chances than any other non-P5 and Boise and Houston have better winning percentages against P5 in the last 8 years.
BYU is 15-23 versus P5 since independence, a 39.5% winning percentage. Before we sulk too much, that winning percentage is better than 99% of non-P5 schools (other than Boise and Houston) and many P5 schools, including Cal and Washington St., and a bunch of others, like Syracuse, Wake Forest, Vanderbilt, Illinois, Kansas, etc.
The Utah losing streak has really hurt BYU's P5 winning percentage.