Per the first link you provided, the F-15 has the following:
Service ceiling: 65,000 ft (20,000 m)
That's high enough to go 15k feet above the highest ballon mentioned in the second link you provided, which was 50,000 feet.
Also, the SR-71 carried no weapons, only cameras, and re-tooling to support them would be far more expensive than merely shooting a balloon with a missile from the ground (or building an air-to-air missile that can be fired from existing platforms at altitudes like 65k feet).
Service ceiling: 65,000 ft (20,000 m)
That's high enough to go 15k feet above the highest ballon mentioned in the second link you provided, which was 50,000 feet.
Also, the SR-71 carried no weapons, only cameras, and re-tooling to support them would be far more expensive than merely shooting a balloon with a missile from the ground (or building an air-to-air missile that can be fired from existing platforms at altitudes like 65k feet).