That´s a long topic. But, in a nutshell:
As you may know, my background is mainly industry and more specifically the automotive industry.
Couldn´t be interchangeable, since here it means "como você deve saber..."https://www.quickanddirtytips.com/education/grammar/because-due-to-since-and-as?page=1“Since they spoke, she’s had second thoughts.” (“Since” could mean “from the time that they spoke” or “because they spoke.”)
In general ways, since
can be interchangeable, more so when they can be replaced by "because"'
So, to my thinking when it means "uma vez que" you can, most of the time, use "since" or "as" interchangeably (beware the above examples, and read what you write before, proofread it for ambiguities, etc.)
With your example, I think "since" is a more apt word, one sees that it means "uma vez que", whereas with "as" it would sound as "como eu estou aqui" (so a slightly different translation for me).
Thus, "uma vez que" focus more on the result than the reason than the latter form; again, for me.
Anyway, I think nobody would sue you for using it!