15 kids?! Are they trying to kill him with pleasure? I get the math, 5 kids for each wife but damn. That's to much
Why too much?
They are a total of only 3.
MC doing it even once a week individually (for a couple of times) should be enough to get them pregnant (in normal situation), and then no sex for 9 months, and then rise and repeat for the next 5-6 years, he would have 15 kids.
And this is assuming they only give birth to one child per birth.