The translation of BG 3.15 that I would make is very close to
Know that action arises from Brahman, Brahman from the Imperishable. Thus Brahman, although all-pervading, is ever established in yajña.
The main point is not to translate 'yajña' as 'sacrifice'. Sacrifice is not an entirely wrong translation of yajña but it is very inadequate. As you would see from BG. 3.9-3.15, yajña is an activity involving two levels--humans and devas--in a mutual nourishment. Of course, my attachment to a lower level prevents me from seeing or listening to the devas and therefore obstructs collaborating with them. Therefore a sacrifice of my attachment to lower levels is needed. But that is only a part of the undertaking. In the exoteric tradition yajña becomes merely an external ceremony with 'havan', 'ahuti', etc.; thus completely perverting the teaching.
In the simple practice of breathing in and breathing out, if I breathe in with more awareness, or as I breathe more consciously, that simply means that I am aware of slightly subtler levels of reality and I therefore invite the deva of prana to assist me, or to work with me, in extracting subtler or alchemical substances from the same air as everyone else breathes. Breathing more consciously is what turns my ordinary breathing into a yajña of breathing-- a prana yajña.
