15 months? Oof.
The bad news: You're not out of the woods.
The good news: The exhaustion starts to get better! (Or maybe you just end up accepting it as the new normal for your existence?)
I think it was around 2 or 2.5 when we noticed we were feeling a lot less of that constant exhaustion. But the COVID lockdown happened when he was about 1.5, so that also kinda threw a wrench in things.