[TheMidnightNarwhal]

She is full of shit. You can 100% disable the CBS thing without doing plugs. In fact the service has nothing to do with plugs AFAIK, for my E92 it's just a general inspection and they would be supposed to then reset the service thing. They probably forgot to reset the light. Idk why they lie to do spark plugs. Maybe you can google a way to reset it yourself, idk if your 2015 can do that but on my E92 I can reset services using the stalk and odometer button. Actually quick google search from guessing your model, seems like it is done the exact same way.

To be fair though, I seriously doubt they deactivated your oil sensor just like that? Don't think it's possible at all with ISTA. Probably broke and you just notice it now. Or maybe they unplugged it considering the bullshiterry they are doing with the CBS notification... hmmm.

OP I hope you find a way to reset the light yourself and call them back and blast them on how incompetent tey are and how a non bmw mehcanic can reset it after doing a 2 minute google search ahahahhaa.