Portuguese Empire 
One cannot credibly claim that the Portuguese Empire began in 1415 with the take over of what ended up being a relatively worthless North African port (Ceuta).  It is consensus that the modern imperial era began with the "discovery" of the Americas by Columbus, 77 years after the capture of Ceuta, which was nothing more than a hop over the straits of Gibraltar for the Portuguese taken for comercial purpose, NOT for empire.  

If the capture of Ceuta in 1415 is to be held as the starting date of the Portuguese Empire, using the same logic, we would then have to (absurdly) argue that the Spanish Empire began with the Castilian conquest of the Canary Islands in 1402.  The Canary Islands were subject to the same colonial pressures that would later characterize European colonization in the Americas (large numbers of colonists with subjugated natives and the overlay of the conquering culture over the conquered one).  Ceuta has much more in common with the Canarian conquest than with a truly imperial expansion.  

Therefore, just as the Spanish Empire began when Columbus landed in the Americas and not with the 1402 take over of the Canary Islands, by the same logic, the Portuguese Empire began with the landing of Cabral in Brazil in 1500, not in some minor North African port in 1415.