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.
Why do people keep on comparing about local legal fiat than to a digital currency? Knowing USD its one of the most strongest currency being used worldwide and talking about of getting replaced by bitcoins seems really impossible even we do say on next 20 years or more.To think of that bitcoin is relying on its value to USD mainly which means it cant really even surpass no matter what an government wont really allow such thing to happen.