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.
Guys be realistic please, bitcoin is just a digital thing. It can't replace dollar, soon or lately. Dollar will maintain to dominate world economy. And nothing can avoid this.
If we are talking about years, 15 - 30 years is not enough, a century is needed before we talk about this.
Bitcoin may be just a digital currency, but now, it is one of the most valued things that even surpassed Gold. The problem is it's volatility or the unstable price which makes many people doubt this digital currency. But as you've said, dollar will maintain and overpower bitcoin no matter what, bitcoin in its current state is not even a worthy competitor of dollar.