There are extremely significant differences between the "original" version of FFXV and the most recent version, and they're somewhat divisive. I'm not sure how you'd experience it though other than playing on a disc version on a console with internet access turned off to be sure to avoid auto-updates, though. Not sure if any of the disc versions come with the updates already patched in or not.
Well, on the whole it sounds like the problems with XV will be the same whichever version I get, so I'll probably just play the updated version and read about whatever the changes are after the fact. I'd just see it as the same thing as being unable to play the original version of XIV. I guess this will be a common problem for people getting into long-running game series in the future, where if they start from the beginning the last games will have changed by the time they get there. Heck, considering how long it has taken me to get this far with Final Fantasy, there might be even more games when I eventually get to XVI.