It's important to remember that, just like XIII, XV would probably had not been made if it weren't labelled an FF because SE pours all the money into its cash cow. SE would not invest so much cash in a completely new IP nowadays in the hopes that it would sell better than any FF. And even if it did, way fewer people would play it. That's why it's pointless to really debate that - even if it had existed in that state, it would not have had the same reach.

Granted, it wouldn't have faced as much criticism as it did. But to be fair, any game that would get the title of "Final Fantasy XV" would be highly criticised by a number of people anyway due to the insane expectations built up for the next numbered title over the years, as well as all the hopes that it will rejuvenate the series after how XIII overstayed its welcome.

It was a no-win situation, and SE made the best that they could. By refining a concept that seemed popular enough and making it as modern as mainstream that they could while still aiming to preserve the Final Fantasy feel (and according to many a reviewer, both fan and critic, they succeeded). And it paid off, considering how much the game sold and that it's been generally very well received.

But that's still not indicative in the slightest of what the next installment will look like, because you can really never expect what the next one will be until it's actually out! So here's hoping it's more in line with yoru sensibilities next time, Fox