Adam Clarke on 2 Kings 20:1

Set thine house in order - It appears from the text that he was smitten with such a disorder as must terminate in death, without the miraculous interposition of God: and he is now commanded to set his house in order, or to give charge concerning his house; to dispose of his affairs, or in other words, to make his will; because his death was at hand. "This sickness," says Jarchi, "took place three days before the defeat of Sennacherib." That it must have been before this defeat, is evident. Hezekiah reigned only twenty-nine years, 2Kgs 18:2. He had reigned fourteen years when the war with Sennacherib began, 2Kgs 18:13, and he reigned fifteen years after this sickness, 2Kgs 20:6; therefore 14+15=29, the term of his reign. Nothing can be clearer than this, that Hezekiah had reigned fourteen years before this time; and that he did live the fifteen years here promised. That Hezekiah's sickness happened before the destruction of Sennacherib's army, is asserted by the text itself: see 2Kgs 20:6.