Only four #15 seeds have ever defeated #2 seeds:
Richmond over Syracuse 73?69 in 1991
Santa Clara over Arizona 64?61 in 1993
Coppin State over South Carolina 78?65 in 1997
Hampton over Iowa State 58?57 in 2001
Since the inception of the 64-team tournament in 1985, each seed-pairing has played a total of 96 first-round games.
The #1 seed has beaten the #16 seed all 96 times (100%).
The #2 seed has beaten the #15 seed 92 times (96%).
The #3 seed has beaten the #14 seed 81 times (84%).
The #4 seed has beaten the #13 seed 79 times (82%).
The #5 seed has beaten the #12 seed 65 times (67%).
The #6 seed has beaten the #11 seed 66 times (69%).
The #7 seed has beaten the #10 seed 60 times (62%).
The #8 seed has beaten the #9 seed 44 times (46%).