15 years? I think even in 30 years we will still be using paper. First Bitcoin has to become stronger and more stable.
15 years is already enough to see that there will be half of the total population of the world will be using bitcoin, crypto currencies and for sure digital currencies or will make transactions automated. I had to believe with it because the world government will have their own currency and will implement the usage of it.
It might be starting in few years. Because as bitcoin showing the value of its one coin then people would easily start investing into bitcoin.
One day it would become a paper as you said. But there are some problem I hope it would be remove on bitcoin as soon as possible. Like one of them is government actions some of government are against bitcoin. But trust me many of country are getting interest in bitcoin now a days. So I hope the restriction against bitcoin remove soon.