Judah's King Amaziah son of Joash lived 15 years after the death of Israel's King Jehoash son of Jehoahaz.
References for 2 Kings 14:17
The rest of the events of Amaziah's [reign] are written about in the Historical Record of Judah's Kings.
A conspiracy was formed against him in Jerusalem, and he fled to Lachish. However, [men] were sent after him to Lachish, and they put him to death there.
They carried him back on horses, and he was buried in Jerusalem with his fathers in the city of David.
Then all the people of Judah took Azariah, who was 16 years old, and made him king in place of his father Amaziah.
References for 2 Kings 14:21
He rebuilt Elathand restored it to Judah after [Amaziah] the king rested with his fathers.
References for 2 Kings 14:22