That's absolutely wrong on so many levels it's hard to know where to start. The US had a higher debt/GDP ratio after World War 2 and it took nowhere near that long to pay it off (and had plenty of people who weren't all about paying off the debt at the helm).
So basically, recent US history decisively disproves this claim.
US treasury bonds underpin a huge amount of the financial transactions that exist worldwide. It would not matter if we did it 'slowly' or 'quickly', because once we telegraphed our intent to not service those bonds massive worldwide financial chaos would ensue. It would be an utter catastrophe.
I think you should read up more on monetary policy and international financial markets.