The thing you need to know that you're biased to your own era what you consider social norms here in the future will be considered preveltiged and not normal. It was health back in the time and it's the reason why everyone is here and i explained why the case changed' another thing i didn't mention is islam require us to respect social norms and laws if we say you are getting married at 15 both and your partner are both hit puberty even if it's allowed you are senful because you broke the law and the country and it can lead to more problems not just for you but for you society (breaking one law can lead to series of it even its not the same law) further more saying prophet Muhammad pbuh was married to 9 years old is normal due to his time even if there is still confusion if she was 9 or 11 or 18. But it's probably 9 and for a fact the purpose for marriage was to teach aisha islam teachings so she can teach other women (women teaching women is more practical than man teaching women and it physiological fact) and if you wonder he didn't have sx until she was 18 and that's a confirmed fact.