John Gill Commentary 2 Kings 18:15

"And Hezekiah gave [him] all the silver that was found in the house of Jehovah, and in the treasures of the king`s house." — 2 Kings 18:15 (ASV)

And Hezekiah gave him all the silver that was found in the
house of the Lord, and in the treasures of the king's house .
] To make up the three hundred talents of silver, for which purpose he exhausted both, which had been done more than once before by the kings of Judah; these were their resources in times of distress; see (2 Kings 12:18) (16:8) .