While 0.15 may seem like a lot, if it's consistent, I'm not ENTIRELY sure I'd worry about it (although I think you'd be well within your rights if a) it's under warranty and it concerns you, and b) it just started when before it was fine to return it, honestly. If you are concerned.
My steampunk nano reads coils high and has consistently done so from the start, and since it's never been a problem, I've never worried and it was one of my first mods. I'd say though, do what feels right to YOU, especially if it has gone from "normal" to "weird."
I have also never heard of this issue for a .Pico, and I have with the steampunk so there is THAT. Etc.
Anna