The subject of 1 Corithians 15 is the resurrection of the dead.
...Christ has indeed been raised from the dead, the firstfruits of those who have fallen asleep. For since death came through a man, the resurrection of the dead comes also through a man. (1 Corinthians 15:20-21.)
If Mary was born without original sin, and bodily assumed into heaven without ever dying, she is not in view here.
And that she entered heaven without ever dying seems to be the earliest tradition.
If it were ordained by God that women should be priests or have any canonical function in the Church, Mary herself, if anyone, should have functioned as a priest in the New Testament. She was counted worthy to bear the king of all in her own womb, the heavenly God, the Son of God. Her womb became a temple, and by God’s kindness and an awesome mystery, was prepared to be a dwelling place of the Lord’s human nature. But it was not God’s pleasure that she be a priest. Like the bodies of the saints, however, she has been held in honor for her character and understanding. And if I should say anything more in her praise, she is like Elijah, who was virgin from his mother’s womb, always remained so, and was taken up, but has not seen death.
Source: St. Epiphanius of Salamis. The Panarion (also known as the Adversus Haereses or "Against Heresies"), Section 79.