I guess the game will be like 15 hours including the TV show episodes, of course that on the first playthrough without skipping nothing, and i'd be fine with that, i don't like when games are longer than they should be, getting filled with useless backtracking or ripetitive and boring mechanics, also it looks like the game will offer different choices at the end of each chapter, which could change the game's story progression, giving also different episodes of the TV show, so i guess we'll be pretty incentivized to replay it
PS: i'd i also think that's why the TV show is 75GB, in my opinion those are not just 4 episodes but at least 8, since you can have two episodes available after each chapter based on the choice you made in the game