15 Above that, the altar hearth is four cubits high, and four horns project upward from the hearth.

Read Ezekiel 43:15 Using Other Translations

So the altar shall be four cubits; and from the altar and upward shall be four horns.
and the altar hearth, four cubits; and from the altar hearth projecting upward, four horns.
The top of the altar, the hearth, rises another 7 feet higher, with a horn rising up from each of the four corners.