Wel you can look up the length of each book put them in a graph and extrapolate. You will probably find they are getting longer.
Yea; and I don't see any reason why that might change in Peace Talks. Look at all the characters and potential plot and subplot threads we can expect to see in Peace Talks:
Harry and the White Council.
I'm not just talking about Harry's status within the Council and how much he's distrusted by some members of the Senior Council. There is also the question of the Council itself. Is it politically fractured or have the Merlin and Cristos come to some kind of (probably temporary) understanding? Will LTW meet with Harry and begin teaching him to control his anger as Eb suggested some time ago?
Thomas, Justine and baby make three are what we know about. What we don't know is how this effects Thomas and Lara's relationship. We also should get a clearer picture of what moves Lara has been making. Plus, some think Lord Raith might start making a comeback or be put down for good. I'm in the later camp, but if anything happens involving LR that will complicate things.
Then there are the Fomor themselves. The Peace Talks are supposed to be about them and their place in the supernatural world. I expect the guy (Lord something or other) Harry threatened in Skin Game to be on hand. Maybe even the Fomor leader (King Korb?) will make an appearance.
What other complication?
Oh yea; Molly, her new
job career, and her parents reaction when they find out.
A teenage Archive and all that may imply as the talk's arbiter. Plus her bodyguard.
Marcone acting as host. No, Gentleman John won't be involved at all. Sure.
Someone unexpected is bound to show up even if they try to remain hidden. Cowl, Mavra, Cat Sith (I don't think so - too soon.), plus we could meet a new major character like Drakul.
I'm sure I've missed other potential plot threads and twists. (Feel free to name them or to make a guess as to what they will be.) So there's no reason to think PT will be a shorter read than Cold Days and I'm fine with that. To my way of thinking this book should be a major turning point in the series. It should lay the ground work that leads us up to the BAT.