I think that the effort to unite the churches might have become stronger in the 15th century because the Empire was no longer a real political and economic riva

I think that the effort to unite the churches might have become stronger in the 15th century because the Empire was no longer a real political and economic rival to Italian merchant republic, Sicily and the rest of the Latin world. It was obvious to everyone in Byzantium that they have no chance of resisting the Turks on their own which made them much more amenable to potential compromise with the church of Rome. The situation was pretty different in 1200, the Empire was in a much stronger position and due to the conflicts with Italian merchant states and the Massacre of the Latins of the Latins just a decade earlier the relations between Constantinople were extremely poor. But yes, even then most probably did not consider the Latin and Greek churches to be fully separate and distinct entities (i.e. the schism was likely closer to the Western Schism of 1378 than to the reformation in how most people perceived it at the time)