..not sure if it's all that much, really. If it's similar to Yakuza 3, then all the cutscenes will be rendered in the game-engine (with the neat face and lip-syncing tech they use to help animate emotion, and so on). About.. 1/3 of it will be interactive. And happen in the middle of a fight, done in a way that make the scenes more interesting (and less hectic to play) than a continuous boss-fight would be.. It's not really "cutscenes" at all, basically..
No.. I don't think 6 hours of cutscenes is a problem. What takes time in the Yakuza games is reading through all the dialogue (with the pop-up boxes). The story-telling that doesn't have voice-acting, and just the generic "talk" animation stances - this can quickly become boring (even though the story is well written).
So if it actually has more cutscenes than Yakuza 3, then that's probably a good thing. If we go by the demo (..which probably still possible to fish from the Nippon store), the reason why it has more cutscenes is that the transitions happen in more real distances, and are tied together in more thoroughly animated scenes. I.e., instead of just fading to black and seeing a car drive off while spawning someone outside a building - you'll get the entire scene, with exiting and entering, suspicious looks, etc. With a good opportunity to drop a few extra Yakuza film tropes in between.
Most likely will be a very fun game to play..
..uh.. if anyone wants to read a review of Yakuza 3, I've written a small treatise on it here:
http://www.honestgamers.com/reviews/8769/Yakuza-3.html
It takes less time to read through than playing the game, though.