1.5mm is a lot of shell face "offness". It's possible, but i question if the shell is OK and the cup was crossed instead. If the shell was not well faced the cup would cock a bit on tightening and the wear path inside would show it's misalignment too. Does the wear path look concentric and even of is it off too? It's pretty easy to cross thread a cup, fine thread pitch for the diameter and often cups or shells have quite partial thread heights.

Now chasing and facing a shell is almost always a good thing to do and this procedure would show if the shell was really off. Buy I would be surprised if the shell was that far off. One can take a machinist's square and lay the body against the shell's face and see how the blade runs WRT the shell's OD. Doing this at a few points around the face will show quickly any major face/shell non squareness. (In fact this is how I faced the first few frames i built back in the late 1970s). If the shell face was off by 1.5mm across it's diameter the square's blade will be close to 3mm off along the shell's side at it's other face. That's a lot and VERY to see.

Do this before you spend $ for a facing job and let us know what is found. Andy.