“I have heard your prayer, I have seen your tears; surely I will heal you” (2 Ki 20:5).
It doesn’t seem that Hezekiah prayed for a longer life, although that goes without saying if the Lord healed him! But 15 years extra? Some think he shouldn’t have asked for more time on earth because during those years some bad things happened. The Babylonians visited the king after his miraculous recovery, and Hezekiah, instead of giving glory to God, showed off his wealth. Later, Isaiah told him the bad news: the Babylonians would return, plunder his treasures, and kidnap his family. He passed the test of adversity, when Sennacherib’s army besieged Jerusalem; unfortunately, he didn’t do so well with the test of prosperity.
The world seeks longer life (though they’ve hardly moved the needle from Psalm 90:10; worldwide, the average life expectancy is 70 for males and 72 for females), but believers seek a fuller life, with “eternity’s values in view” and in fellowship with the One who always knows best.