] I noticed this line in P2, which I believe was spoken by Lady Russell. Someone then asked if "Sir William" had spoken at the event in question. Could they have been referring to William Paley, the great Christian apologist who lived at about JA's time? I do not think this line was in the book, and I was just wondering.

No, I don't think the line was in the book either. It seems to be filler to reflect the idea, which is established in the book, that Lady Russell enjoys the lectures and other such pleasures of Bath.

One clue, if it helps, is the opening line in this exchange when Lady Russell asks, "Did you attend the Philosophical Society?" Whether this would be a discussion group or an organized debate I don't pretend to know, but it does seem to be an event at which ideas are exchanged with spirit, rather than a straight lecture.