You misread your source: the F-15 can climb 30,000 feet in 60 seconds - the service ceiling is closer to 60,000 feet officially, and 90,000 under ideal conditions:

https://theaviationgeekclub.com/how-the-f-15-streak-eagle-br...

By "same altitude" I was referring to the SR-71. I do not know what the payload capacity was for either aircraft in the 90,000ft testing conditions, but for interception missions there are more important metrics.