I believe I touched on all of your points in my post above - yes, I agree, lots of questionsThere is one major part of this story missing. What was the response when the OP said, "look, I know this car, it LIKES 15w-40, put that in after you do the service, thank you". The story jumps from that to getting the car back home. The integrity of the shop weighs entirely on what that response was. If they said, "No, I'm sorry, we can't do that." then that's completely different then if the service writer said, "Yeah, sure, we can do that." and then didn't do it.
Another major part of the story missing here is how did the OP know it was 5w-20? That's left out. Does it say that on the work order? If so, why wasn't this seen while still at the shop where you could have brought it up to the service writer? If the OP knows this was 5w-20 just by pulling the dipstick and looking at it, that's sounds pretty sketchy. There's no way you can know with enough certainty to condemn a shop just by looking at some oil on a dipstick.
And then not checking oil for 2 months when you supposedly know it's going to burn faster. You don't "get busy for 2 months". Just say you forgot to check it. It happens. We're all human. You're allowed to forget to do things.
I just see a lot of people filling in the blanks on their own here based on their own biases. I'd like more information before passing judgement on someone.