John Gill Commentary 2 Kings 15:4

"Howbeit the high places were not taken away: the people still sacrificed and burnt incense in the high places." — 2 Kings 15:4 (ASV)

Save that the high places were not removed
That is, he did right, excepting in that instance, and which was the case of his father and other kings before him, and others afterwards, till Hezekiah came:

the people sacrificed and burnt incense still on the high places ;
see (2 Kings 12:3) .