Question

How long did the changes of the congress of Vienna last

Answer 1

The Congress of Vienna helped to prevent another major war in Europe for nearly a hundred years (from 1815 to when WW1 started in 1914). In short, it established changes that maintained the balance in Europe between the major powers.

The downside is that it also ignored the democratic and nationalistic yearnings of many others, something that would come to haunt Europe many years later. It was a very heavy handed solution to peace.