I'm glad it's PG-13, because that means it'll definitely be M in Australia. If it was any higher, it would likely have been restricted to 15 years and over which means I'd be the only sibling in my family able to legally watch it without parental supervision despite us all liking the film. And, if it was 18+ I wouldn't be able to legally watch it at all.
People who wanted it to be 15+ or 18+ don't understand that FNAF isn't just for adults. While I'm wary of young viewers and children watching the film, adolescents and preteens should be able to watch the film too. I know for a fact most of us grew up on the series, and telling someone who used to be YOU that they shouldn't be able to watch the film they've been waiting for just doesn't sit right with me.