I feel like I'm blanking on an event somewhere. We know that the major events for three of the next four chapters are mostly going to include the vacation to Perry's beach house, Billy's photoshoot, and the MMA tournament. Since the photoshoot is basically exclusive to Lena and the MMA tournament is pretty exclusive to Ian I could see these two happening in the same chapter. We're still waiting on the results of Ian's writting competition, and recently introduced is Lena's music competition, which again these two could probably be combined to form a chapter's worth of plot.
Smaller subplots that can be resolved or sprinkled in throughout these upcoming chapters: anything involving wildcats, Lena dancing at the club, another civic center event, the results of Ian's recommendations for publication, the mystery surrounding the homeless man, potentially Holly and Robert.
So what am I forgetting that can fill in chapter 15? Assuming that chapter 16 will be the wrap-up chapter now.