Is it part of God's Promise to Abraham and his seed?
I asked, “Does that include Gen. 15:18?”
You then asked, Is it part of God's Promise to Abraham and his seed?
What is the subject of the pronoun "it"?
If by "it" you are referring to the promise in Gen 15:18, then I would say "yes". The promise of Gen. 15:18 is part of the promise to the "Seed" of Abraham, and is fulfilled entirely in the gospel, since we know from Galatians 3 that the "Seed" to whom all the promises were made in Jesus Christ, not ethnic Israel.
It is in Christ, the only true and faithful Seed of Abraham, that all the nations of the world are blessed. It is the new Jerusalem, where Jesus Christ now reigns on the throne of David, that Abraham was longing, not a tiny piece of ground in the middle east (Heb. 11:16).
Ethnic Israel is blessed only insofar as they are found to be in Christ. In order for them to prove themselves to be true sons of Abraham, they must be found in Christ and also have a longing for the same promise of a heavenly land, not the carnal one. Then they are part of the true, spiritual Israel of God.