Disclaimer: without measurements, this is pretty hard.
I’m disinclined to class it as a min’yo shamisen. Min’yo shamisen use what’s called a go-rin-dai body and a chuuzao neck (2.6 - 2.8 cm wide). That’s the second from the left in the attached image.
The shamisen on the right in your images is a little bit smaller than the one on the left - or seems to be. However, I don’t think it’s small enough to meet go - rin - dai sizing. The neck may be a chuuzao however.
It seems to me that it’s a 1分5厘大 (ichi bu go rin dai). This is the sizing used in chuuzao and jiuta shamisen. It may also be an interim value between 1.5 Bu Dai and 5 Bu Dai. Particularly, 2 Bu Dai is relatively common in Jiuta.
As well, some Tsugaru are built with smaller players in mind and utilize customized sizes, so one occasionally see 3.5 bu dai and all that.