I honestly don't think it'll happen, certainly not in 15 years... In 100 years maybe?
I don't think the problem is technology- we already are extremely close to being able to replace the dollar in that matter, due to smartphones. The problem lies with government control of money, and the legal guarantee and security (stability-wise) that it brings. If smartphone technology becomes cheaper, I think we may see countries with unstable dollar value using it more.
It's actually makes sense but since bitcoin transaction required internet access
There a lot of places that not yet covered by internet access then having smartphone will mean nothing
I think the same that it's not impossible for bitcoin to replace dollar
But of course not in the near future, not soon.