Interesting, Reinhold. I guess the benefit of shooting 6X15 instead of shooting 6X17 and cropping is that you can get more images per roll of 120 film? FYI, Film and Darkroom User requires me to sign up as a member to view your photos.
Ditto here. Even though I don't yet own a panoramic camera I've long thought that this intermediate format would provide the Goldilocks aspect ratio for me, with 6x12 being typically not quite panoramic enough and 6x17 being just a little too wide for my tastes. Since we're talking about camera modifications here, I should point out that anyone interested in making a DIY panoramic camera by converting an old folder to use 120 film, any of the "No. 3A" Kodak or Brownie cameras are what you need to yield nominally the 1:2.5 aspect ratio.
FWIW, a long time go I made a 6x14 camera out of a horizontal 3A Kodak. http://www.paulewins.com/blog/?page_id=89 I love that format although nowadays I'm more likely to be cropping or stitching digital files.