2 Kings 20:6

And I will add unto thy days fifteen years
(See Gill on Isaiah 38:5)

and I will deliver thee, and this city, out of the hand of the
king of Assyria;
by which it appears that this sickness and recovery were before the destruction of the Assyrian army:

and I will defend this city for mine own sake, and for my servant
David's sake:
for the sake of his honour and glory in the temple, and the service of it, that were in Jerusalem, and for the sake of his promise to David and his seed.