I would say it’s difficult to map to JLPT terms because the JLPT is unlikely to cover organized crime slang, dialects, or things yelled during a street fight. 
Since the games cover so much ground both in the main plot and side activities, there’s also just a whole lot of vocabulary in general across many subjects.
At the extreme, stuff like restaurant food descriptions or mahjong, etc. can be stuffed with speciality vocabulary (but can be avoided without compromising any of the story). For the main stuff, understanding contractions and epithets often used by aggressive men + some basic vocabulary around yakuza organizations would probably be the biggest obstacles.
There’s subtitles for everything though (without furigana).
When I played 7 in Japanese, I spent a whole lot of time pausing (note: in 7, and I think most games in the series, I remember the subtitles in cutscenes thankfully being visible when paused - I remember this not being the case with Lost Judgment though) looking up words on my phone. At the time (I had completed WK but not done very much vocabulary mining and reviewing outside of it) I would do this pretty much constantly and the amount just slowly decreases with each game I play this way (I’m dabbling with Kiwami 2 now and I think it’s my… fifth? in Japanese and I wouldn’t say I have to look up very much at all, but that’s been a long time coming…).
But I played 7 at a time when I thought for sure I wouldn’t be ready, and I’m really glad I did since I learned a ton and gained a whole lot of confidence from the process (and loved the game)!
So the high level of vocabulary can be a positive, since it’s a very fun way to jump into the deep end, so to speak, and get exposure to a lot of different topics.
Instead, I read another chapter of よつばと！ – chapter 15. Asagi has been a direct or indirect focus for a few chapters now, so I feel like something’s cooking.
Today, people can bring their old needles (stabbed into tofu or konjac) and offer them at a shrine while praying for better sewing skills.
