What about Memorial High School (Memorial at Dairy-Ashford). That’s pretty big - and it was build over 25-30 years ago.
https://cms.springbranchisd.com/athletics/For-Parents-Students/Facilities-Maps/Darrell-Tully-Stadium
I think you are referring to Tully Stadium built in 66’ on Dairy Ashford for $1.2 million.
15000 seats.
Biggest in Texas (not counting Toyota Stadium in Frisco) is Memorial Stadium in Mesquite. Built in 1976. Seats 20k.