Section Z15 is not a part of chairback seating, which is primarily found on the North upper level and the sideline club seats.
Like neighboring sideline seats, the corner sections are gigantic and can contain more than 60 rows of seats. Sections G, H and I are notorious for being directly in the sun and are typically reserved for students and the band.
Rows 30 and higher will give you a better view of the field than being down close. For best views of the scoreboard, avoid G-I and O-Q.
Section Y10-Z15 are typically given to opposing team fans.