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!
Claiming on a point without comparison may lead on misconception. Between bitcoin and fiat there are things that may compare both of them. First we all know that fiat is a tangible thing that we can hold literaly and bitcoin is intangible that can be mamaged through transaction in internet meaning to say web base and wallet base holding. Maybe some can say that bitcoin can replace dollar on transaction because people will choose bitcoin because it has fast and reliable transaction. But in a world full of regulation especialy the government and the legality it maybe questionanle due to lock of transaction confirmation and information. But we all know that bitcoin itself is a good investment making it a great choice between fiat.