All the years from a. d. 1400 to a. d. 1499 make up the fifteenth century a. d. true or false?

False.

Explanation:

It is actually false that all of the years above belong to the 15th century AD. In reality, the fifteenth century begins during 1401 AD, which means that AD 1400 still belongs to the fourteenth century.

Similarly, year 1500 belongs to the fifteenth, rather than sixteenth century, which will begin in 1501, and so on.