Claims like this are fun to talk about but little more than good marketing for Coinbase. (Don't get me wrong, I like Coinbase). But no one can say for sure whether bitcoin will have staying power and significance to be considered the world's reserve currency ever let alone 15 years.
What I think is a better discussion to have about this is why would we want Bitcoin to be the world's reserve currency. Existing fiat currencies are controlled and manipulated by Governments and Banks. Do you think these people are going to just let Bitcoin exist without their involvement or blessing? Do you think these people aren't going to want to have control and option to manipulate Bitcoin as they have fiat?
I think the answer is No!
If Bitcoin becomes the world's reserve currency, Bitcoin will be destroyed as we know it. I can't see a way that it wouldn't, but if you all think differently I'd love to hear it!
I agree with the advertising part. When i read OP's post the first thought that came into my mind was "wow coinbase really believes in bitcoin, i should start using their wallet again" lol.
But IMO i don't think bitcoin is going to replace the dollar anytime soon, not within 20 years anyways. Fiat is just wasier to transact in person. Bitcoin works well for transactions that take place over the internet and its all about the ease of use.