Chapter 16 calls upon the Moabites to send the lamb of the ruler of the land to the mount of the daughter of Zion, because the throne of David shall be established and the oppressor will be consumed. The lamb is evidently an acknowledgment of subjection to Israel. (See 2 Kings 3:44And Mesha king of Moab was a sheepmaster, and rendered unto the king of Israel an hundred thousand lambs, and an hundred thousand rams, with the wool. (2 Kings 3:4)).
As to the chastisement then to fall on Moab, verse 14 names the time as three years distant, and its severity so great that of that great multitude but a remnant should be left. Scripture does not say at whose hands this infliction would occur. It may have been the Assyrian of that day.
In the future day they will escape the armies of the Assyrian, perhaps because thought of too little consequence to bother with them, but they will be dealt with by restored Israel.