depth under keel almost zero - shallow waters quite off the coast

[Pisces]

The channel north of the Isle of Skye, where you are, is not what I would call open sea yet. So 15 meters of depth isn't so strange. Then again, the fjords of Norway are pretty deep in real. Not what you would expect inland.

Google Earth does give depths between 50-150 meters in that region. So the SH3 maps are definately not hi-fi(delity).