Could my iPhone have been hacked, when I didnt installed IOS15.3?

Hi, I'm a bit confused, in IOS15.3 the biggest security update mentioned is this Safari bug, but what about 'memory corruption bug'? That lets hackers access your phone. That's usually not mentioned at all. Or does that only apply to some iPhone users? I think that's a lot worse. And if you were hacked, was that fixed with the new update on infected phones? I installed this update 2 days later :/