V15 messed up my banglejs ?

[0,16]

Ok, that's good - it means you have the slightly newer variant with the SPL06 barometer in, and that the barometer is communicating fine with the watch.

After going back to 2v14 it still reads 0.

Ok, so I think that 2v15 was a bit of a red herring then. Please could you try:

• Install 2v15 again
  
• Ensure all the apps are up to date
  
• Go to Settings -> Utils -> Flatten Battery and leave the Bangle off-charge for several hours to flatten itself.
  
  

Put it back on a charger and long-press the button to restart it after an hour or so.

Having a full power cycle done actually be enough to bring the Barometer back. It's possible that somehow during the flashing process it just got itself configured wrong and it'll need a power cycle to refresh itself.