Did educated 15th century Europeans believe the Earth was flat?

No, educated Europeans in the 15th century did not generally believe that the Earth was flat. By this time, many scholars were aware of the Earth’s spherical shape, a concept dating back to ancient Greece. The idea of a flat Earth was largely a misconception perpetuated in later centuries, rather than a reflection of 15th-century thought. Prominent figures, such as Christopher Columbus and others, understood and accepted the Earth's curvature in their explorations.