I think that you could argue that the most important technological advance during this time was the invention of the printing press by Johannes Gutenberg. I guess this was technically invented a bit before 1450, but the first Gutenberg Bible was printed in 1456.
With the invention of the printing press, books and other types of printed stuff could be created much more cheaply. This spread learning so much faster than was ever possible before. Because of this, I think that this could well be the most important advance of that time frame.