Of course i thing in 15 years bitcoin will replace dollar 
I don't think the predictability of bitcoin prices prevents its use as a reserve currency. Who can predict the exchange rate of bitcoin a year from now? And the dollar is more or less clear. It will not let bitcoin displace the us dollar.Dollar, too, no one can predict exactly in a year, but it has the advantage over bitcoin in that it is used by more people and for this they do not need the Internet.