What a difference! I read cap 15 and was thinking, “hey, I’ve got this latin licked”. I just read cap 16 - well, skimmed over it. I mean, I get the gist of it, but I feel like a complete novice. I don’t know if I’ve just lost the plot, but it seems to be all new stuff. To be quite honest, it’s making me wonder whether I want to carry on.
Capitulum Sextum Decimum is just where it starts to get interesting! Medus et Lydia! I recall a few really difficult bits, however, that became easier on a later reading. Somewhere around that point of the book, I went back to the beginning and redid all of the exercises.
Dude, don’t give up…believe me that LLPSI is really worth the effort, I’m telling you from my experience…at the moment I’m reading Ritchie’s Fabulae Faciles after Familia Romana, without any problem. I already read Fabulae Syrae…
Insist a little more, if you find difficult passages you can resort to sites like this, an oral translation of Roman Family:
http://www.lingvalatina.com/p/llpsi-translations.html
It is not desirable, but perhaps in your case it will help you get ahead. Do you already have Jeanne Marie Neumann’s A Companion to Rome? it is very helpful too. 
Having now read it 3 times, I can say it’s a bit less intimidating.
BTW, is that a bible hidden in her skirt?
Praeterea Lydia parvum librum fert, quem sub vestimentis occultat.
It sure seems to be (well, at least a Psalter or whatever small codex Gospel/Epistle a Christian might carry). Foreshadowing the big reveal later in the chapter of “Serva nos, domine!” while everyone else calls on Neptunus.
LLPSI can be a bit of a roller coaster. Some chapters introduce heavy grammar, some are a breeze but have lots of new vocabulary. Personally, I hit a wall at chapter 23 when I realized I had to start memorizing the principal parts of all the verbs. My daily flashcard review ballooned from 70-90 to over 160 until I started to get a handle on the patterns for conjugations II-IV for all of the words I thought I had previously “learned”.
But stick with it.! Iʻm on Chapter 25 when Syra starts narrating myths to Quintus and it a real delight. I feel like Iʻve actually moved beyond the McGuffey reader phase, and Iʻm reading “real Latin”. Iʻm looking forward to starting Fābulae Syrae shortly.