Aldav53, I need some clarification, in your first post you ask,
Has anyone seen or installed 15 amp circuits in commercial buildings?
and then in your second post you say,
The reason I ask is someone added some walls and wired some church offices in 14-2 romex. Probably be ok, not much load there. The walls are wood construction too. I could change the breaker to a 15 amp.
What you appear to have is # 14 over fused and in violation of 240.4(D), you must change the breaker(s)
With that said, there is no problem as far as the NEC is concerned with having 15 amp circuits in commercial installations if the wiring meets or exceeds the OCPD.
Even in areas where #12 is the minimum size conductor for branch circuits or feeders it would not prohibit protecting the conductors at 15 amps or lower, and infact, certain equipment may have a Max circuit protection below 15.