Jehovah’s Witnesses teach that Michael the arch-angel is Jesus. So did Michael swear the oath to Abraham at Genesis 22:15-17?

You say: “Jehovah Witnesses teach that Michael the arch-angel is Jesus.” This is true. The booklet What Does the Bible Really Teach? says this in the Appendix on pages 218-219:

“Likewise, the Bible indicates that Michael is another name for Jesus Christ, before and after his life on earth.” After quoting 1 Thessalonians 4:16 it says: “This scripture therefore suggests that Jesus himself is the archangel Michael... it is logical to conclude that Michael is none other than Jesus Christ in his heavenly role.”

You say: “So the Jehovah's Witnesses belief that Jesus appears in the OT is primarily based on Jesus identity as "The Word" as well as the OT wording "Jehovah's angel." This is true according to this article, The Word – Insight on the Scriptures, Volume 2:

“It is reasonable to think that prior to Jesus’ coming to Earth, on many of the occasions when God communicated with humans he used the Word as his angelic mouthpiece. (Ge 16:7-11; 22:11; 31:11; Ex 3:2-5; Jg 2:1-4; 6:11, 12; 13:3) Citing a number of scriptural citations, the article assumes that Jesus was the angel that: stopped Abraham from sacrificing Isaac; spoke to Moses through the burning bush; may have been the angel that was charged with leading the nation of Israel through the wilderness. In all except the latter case, the scriptures referenced specifically mention "Jehovah's angel." https://wol.jw.org/en/wol/d/r1/lp-e/1200004625#h=31

Another article I found sheds some light on your question. This is a partial quote from an article about Jesus Christ – Prehuman Existence - Insight on the Scriptures, Volume 2, page 52. Jesus Christ is “The name and title of the Son of God from the time of his anointing while on earth.”

“Doubtless on many occasions during his prehuman existence as the Word, Jesus acted as Jehovah’s Spokesman to persons on earth. While certain texts refer to Jehovah as though directly speaking to humans, other texts make clear that he did so through an angelic representative. (Compare Ex 3:2-4 with Ac 7:30, 35; also Ge 16:7-11, 13; 22:1, 11, 12, 15-18) Reasonably, in the majority of such cases God spoke through the Word.” Jesus continues to bear the name “The Word of God” since his return to heavenly glory.—Re 19:13, 16. https://wol.jw.org/en/wol/d/r1/lp-e/1200002451#h=1:0

The articles say that with regard to Genesis 22:15-18 Jehovah “used the Word as his angelic mouthpiece” and “texts make clear that he did so (spoke) through an angelic representative.” They do not say that it was the Word, or an angel, who swore the oath to Abraham; the oath was “the utterance of Jehovah” (Genesis 22:16 NWT).

As far as I am aware, they do not say that Michael the archangel is the Word, although they do say that the Word was Jehovah’s angelic mouthpiece. The point is they say both the Word and Michael are created, that they had a beginning. They say the Son of God was only known as Jesus while on earth and that he is known as both Michael and the Word before and after his human existence. They also say that it was the spirit of Michael that entered into Jesus before he was born. They claim that the body of Jesus was disposed of by Jehovah God, dissolved into its constituent elements or atoms. Source: https://wol.jw.org/en/wol/d/r1/lp-e/1953641?q=resurrection+jesus+body&p=par

The man, Jesus, is dead – forever dead – that what came out of the tomb was a spirit creature – Michael. Which rather begs the question, who is coming back? A created angel called Michael?

Edit – Here is the quote that is causing me considerable confusion about the beliefs of Jehovah’s Witnesses with regard to the relationship between Michael the Archangel and Jesus: "Who, though, was the son whom God chose to be born as a perfect human creature? ...He has rightly been called Michael the Archangel. His life-force having been transferred to Mary's egg cell by Almighty God's power that overshadowed Mary meant that he, Michael, disappeared from heaven. By human birth from Mary, the Jewish virgin, he was to become a human soul." (God's Eternal Purpose now Triumphing, 1974, pp 137-138)

Jesus is Michael is his pre human existence in heaven and his post resurrection heavenly existence.

“The Word”is a title belonging to Jesus as well.

Jehovah alone is the Almighty God and Creator.

In regards to the promise made to Abraham in Genesis22:15-18

15 And the angel of the Lord called unto Abraham out of heaven the second time, 16 And said, By myself have I sworn, saith the Lord, for because thou hast done this thing, and hast not withheld thy son, thine only son: 17 That in blessing I will bless thee and in multiplying I will multiply thy seed as the stars of the heaven, and as the sand which is upon the sea shore; and thy seed shall possess the gate of his enemies; 18 And in thy seed shall all the nations of the earth be blessed; because thou hast obeyed my voice.

A careful reading of these verses makes it clear that the angel of the Lord (YHWH) is a messenger delivering the promise that The Lord (YHWH) is swearing on Himself to fulfill in behalf of Abraham.

Whether that angel is Jesus or some other angel is irrelevant since the oath is made by YHWH to Abraham. The messenger is not swearing an oath personally nor by proxy. The angel is bringing YHWH’s words, not his own to Abraham.

Think of an attorney reading your grandfather’s last will and testament in which your grand father promised that you are to receive all of his earthly belongings upon his death. Your grandfather commissioned the will, expressed his wishes in it and signed the document in the presence of the attorney. After it is read you understand that you are inheriting your grandfathers estate. The attorney has promised you nothing.