Proto (from Protos) - first Kotos (from Tikto) - to bring forth
While the first one to brought forth of a class in the Bible is given preeminence, the word firstborn does not at all mean preeminent. The word "firstborn" -- all the way through the Bible -- always means the first one of the group to be brought forth into existence.
While the right of the firstborn could be transferred to another than the actual firstborn, in no case do we read that one who obtained such a right was never brought forth into existence as a member of the group being referred to.
In the case of Colossians 1:15, the group membership is that of "all creation", as defined in Colossians 1:16. There is no indication that Jesus took the place of someone else who was the actual first one to be brought forth of all the creation being spoken of. He was the original one -- the actual firstborn -- the actual first one to be brought forth into existence, of all the creation being spoken of. This is what gives him the right of preeminence.