But my understanding of those number is that that number is usually just retirement savings (they sometimes include employer match on 401K, but sometimes don't in that 15% number)

But that 15% rarely if ever includes paying off debt, which is something that you suggest should be included in this calculation. I think that's probably right to think about paying down debt as wortwhile in calculating your savings rate. I just don't think recommendations of 15% ever include paying down debt.