This verse, together with 2 Kings 14:16, is almost word-for-word identical to 2 Kings 13:12–13. These are the customary descriptive endings of a king and his reign.
Concerning the announcement in 2 Kings 13:12–13, it is strange that it is written there, as there will still be a lot more told about Jehoash. The concluding formula in this verse also appears in a strange place, for the announcement is about Jehoash, but the focus of our passage was on Amaziah and how his reign went.
But there is some substantive connection with the foregoing, for that was about how Jehoash acted in the war with Amaziah.
15 Now the rest of the acts of Jehoash that he did, and his might, and how he fought with Amaziah king of Judah, are they not written in the Book of the Chronicles of the Kings of Israel?