I don't think  bitcoin will replace dollars that soon. Because as of now bitcoin still fighting It's legalization and not all country recognized bitcoin . But maybe your right it's takes 15 years or more to make things happen. But Hopefully even bitcoin will not be the world currency atleast it will last life time for our benefits. We benefited bitcoin even its not yet legal in our countries. The possible thing is that we earn, and bitcoin help each of  as and our family  needs.