I don't know for fact what the precipitate is but I'm certain it isn't silver chloride. If you had chloride in the water or nitric acid it would have formed a cloud of silver chloride whenever you added more water or nitric to the beaker.
According to http://www.harrisproductsgroup.com/en/Products/Alloys/Brazing/Phos-Copper/Stay-Silv-15.aspx the braze consists of :
Cu - 80%
P - 5%
Ag - 15%
Phosphorus in nitric acid apparently turns into phosphoric acid. That should react with the copper in solution and form Cu
3(PO
4)
2, an insoluble phosphate salt. After some more reading I realize that it should form Cu
2(PO
4)OH, the green hydrated copper phosphate salt. Still, it's insoluble in water.
Let's see what happens with the silver in solution... Silver phosphate, Ag
3PO
4 is only slightly soluble in water (mg/liter) but more soluble than the copper phosphate. With a lot of copper nitrate in solution the reaction should move towards silver nitrate in solution and copper phosphate as a precipitate. How fast this reaction goes, I can't tell, but it can take significant time so I should expect some silver also precipitating with the copper.
This is just speculations on my side, backed up with some research online. Let me know if you think I'm wrong or if I have drawn some false conclusions.
https://en.wikipedia.org/wiki/Copper(II)_phosphate
https://en.wikipedia.org/wiki/Silver_phosphate
TLDR; The precipitation is probably mostly copper phosphate.
(TLDR = Too Long, Didn't Read.
)
Göran