I agree with what others have said, but I also think JA is mocking other novels again. The whole paragraph is:

This brief account of the family is intended to supersede the necessity of a long and minute detail from Mrs. Thorpe herself, of her past adventures and sufferings, which might otherwise be expected to occupy the three or four following chapters; in which the worthlessness of lords and attornies might be set forth, and conversations, which had passed twenty years before, be minutely repeated. (chpt 4).

Who can remember all the details of conversations that took place 20 years ago? But sometimes novels do pretend that their characters can. And novels can be quite long-winded and spend several chapters relating the misfortunes of some periphial character (unfortunately all the examples I can think of off the top of my head, like _Les Miserables_, are written after JA's time).