The feminists will tell you that a grown adult dating a 15 yo is wrong because the adult is more powerful and can easily manipulate the minor. They believe it's wrong because it's anti-egalitarian.

However, the red pillers fundamentally reject egalitarian relationships and actually believe dominating and (slightly) manipulating women is a good thing. This is why in patriarchal societies they thought nothing of a 15 yo marrying someone older.