The problem is we have a fairly large interest payment, and our debt is financed on a relatively short term.
So if (when) our borrowing costs finally increase, there will be a whipsaw effect where our interest payments dramatically increase which then increases our deficits and debt which in turn increase our borrowing costs, etc. etc.
But you are right -- we could print-up $15T dollars tomorrow morning and pay off the debt in a day. But that's a one-time ever maneuver.