May I ask what your Xbox username is? I would be curious to check if you actually do have these achievements. I've seen literally not one person with them, and this trueachievements website specifically scans Xbox profiles for achievement unlocks, so when a specific achievement says "0 users have unlocked this achievement" it is accurate at least to the people who have linked their accounts.There are plenty of people (myself included) who have every achievement on the PC version.
It’s possible some are bugged in the current version, but this website appears to have made up the “15 are unobtainable” number.
The list on the side that lists how many achievements are unobtainable are user-reported, so it's not always absolutely accurate.
Personally I play on the Windows store version of the game and I love obtaining achievements so I've been hoping for this to get fixed for awhile now.