Take a look at the team that beat ASU in 1997.
To attain a top 15 ranking you need to be a major conference team with 3 losses or less. Or a nonmajor team with 1-2 losses.
We've had plenty of opportunity.
Just to name a few, if we beat ND in '12, TCU in '09 or'10, Utah in '04 or '08, USC in '03, FSU in '00, Tulane in '98 they would have still finished in the top 15.