i didnt read all the thread pages, but oil is still good if a UOA says so. no need to swap out the oil (synth or other) until there is a reason to do so. OEM suggestions are very over-aggressive in their recommendation of mileage & time intervals, which is ok, just costs you more $$.
i use all 3 of my vehicles for about 12k mi per year. all go 1yr/7500mi minimum, and with some recent UOA's i will be going longer. i use Valvoline full-synth oil.
a filter however should be done more often because thats the item that traps the dirt.
as for 15k for BMW, sure, its possible, a UOA probably shows their oil is fine at 15k miles.
so what you see on paper can only be backed by UOA's, otherwise its just print on paper, etc.