The passage you refer to is only till the end of the world Revelation 11.15 and 22.1 show that the Father Reigns Jointly will with Jesus
Revelation 11:15
And the seventh angel sounded; and there were great voices in heaven, saying, The kingdoms of this world are become the kingdoms of our Lord, and of his Christ; and he shall reign for ever and ever.
The words "he shall reign" is singular in the Greek. Showing the one Reign of both Father and Jesus. Same in 22.1 where the word "throne" is singular
this is where you err.
The reign is of the millenial reign of Jesus where He reigns supreme until the 1,000 year kingdom is over. After the 1,000 year reign is over:
Rev. 20:
7 And when the thousand years are expired, Satan shall be loosed out of his prison,
8 And shall go out to deceive the nations which are in the four quarters of the earth, Gog, and Magog, to gather them together to battle: the number of whom is as the sand of the sea.
9 And they went up on the breadth of the earth, and compassed the camp of the saints about, and the beloved city: and fire came down from God out of heaven, and devoured them.
10 And the devil that deceived them was cast into the lake of fire and brimstone, where the beast and the false prophet are, and shall be tormented day and night for ever and ever.
11 And I saw a great white throne, and him that sat on it, from whose face the earth and the heaven fled away; and there was found no place for them.
12 And I saw the dead, small and great, stand before God; and the books were opened: and another book was opened, which is the book of life: and the dead were judged out of those things which were written in the books, according to their works.
13 And the sea gave up the dead which were in it; and death and hell delivered up the dead which were in them: and they were judged every man according to their works.
14 And death and hell were cast into the lake of fire. This is the second death.
15 And whosoever was not found written in the book of life was cast into the lake of fire.
After the millenial kingdom but before eternity, the great white throne is established and death is destroyed in the lake of fire. Once death is destroyed then this happens according to Gods Word:
1 Corinthians 15:25-28
King James Version
25 For he must reign, till he hath put all enemies under his feet.
26 The last enemy that shall be destroyed is death.
27 For he hath put all things under his feet. But when he saith all things are put under him, it is manifest that he is excepted, which did put all things under him.
28 And when all things shall be subdued unto him, then shall the Son also himself be subject unto him that put all things under him, that God may be all in all.
Once Jesus has subdued all things and destroys death- Jesus submits HImself to the Father and sits at His right side as second most High King under His Father.