Im going to assume right now since i've never used one of the Chocobo set.
I'd have to say it's in RL minutes. Game minutes would be less then a RL minute. 1 hour in Game Time is equal to 3 minutes, about. So, with the full Chocobo Set on, you'd get an additional 15 minutes in Game Time, which would only give you an additional 45 seconds in RL.
That could be good, and it could be bad. Either way, it's more time to ride a chocobo. Although, the extra 15 minutes RL is probably the time given, since getting from Jeuno to Bastok on chocobo allows no time for mistakes, albeit, there is a Chocobo "Handler", if you will, at each of the many Crags.
You're right, the full set adds approximately 15 minutes. Added to your normal riding time (20mins?) you can get pretty far on a chocobo. But this stuff is really those who want to raise their "Chocobo Dig" skill; the longer you're on the choco the less you have to run back and get another. Don't ask me about the 'Dig skill', I know almost nothing about it.
I don't think that it takes the full time on the chocobo to get to Bastok from Jueno, becasue I have made it several times from San d'Oria all the way to Windurst on a single chocobo, and that is without messing up. I've gotten lost once, and I ended up getting kicked off the chocobo in the middle of W. Sarbuta (zone right out of windurst). Are you just following the path, because the paths wind around a long distance and it's faster just to go straight, or was there a patch update that added on more chocobo time?
from what I've been able to do, shortest time to Jeuno from Bastok is somewhere between 18-19 minutes. Unless there's some shortcut in Rolanberry Fields I don't know about. Unfortunately, that leaves barely 11 minutes to make it to Windurst from there, and THAT leaves you stranded high and dry just before the zone to Sarutabaruta. From our calculation, we were missing around 4-5 minutes riding time to make it from Bastok to Windurst on Chocobo... so more than likely, only one piece of Riding gear would have been sufficient for the complete trip (assuming we don't stop to dig, or get caught up in groups of players or mobs, or those damned annoying Rolanberry vines....)
Making the run without chocbo set from Bastok to Windurst, I was able to zone into sarutabaruta @ 30:16, and rode for about a minute and a half more, getting off just after crossing the east<->west river. One piece of riding equiptment would have been sufficient.
And for the record, Bastok to Sauromogue was made in 15 minutes flat. Had I found the right turn in Tahrongi Canyon to make the shortcut I might have shaved a minute more; but that still would have fell short of the goal.