Jamieson, Fausset and Brown on Ezekiel 17:15

15. he rebelled--God permitted this because of His wrath against Jerusalem (2Ki 24:20).

horses--in which Egypt abounded and which were forbidden to Israel to seek from Egypt, or indeed to "multiply" at all (De 17:16; Is 31:1, 3; compare Is 36:9). Diodorus Siculus [1.45] says that the whole region from Thebes to Memphis was filled with royal stalls, so that twenty thousand chariots with two horses in each could be furnished for war.

Shall he prosper?--The third time this question is asked, with an indignant denial understood (Eze 17:9, 10). Even the heathen believed that breakers of an oath would not "escape" punishment.