Oh jeez.. I'm in the 2 unit boat for Shirutin's party as well and have no earlier save to try to get any of the other units. 16 seems doable, even if it's been a bit rough so far, I'm going to call it a night on turn 5, Chapter 15 took a bit too much out of me.
I was contemplating a replay of the game now that I have some idea of what's going on, but it'd just be too painful after I'm already 20 hours in. I'll try to trudge through the demonic chapter 17 later in the week, but the game is starting to burn me out with this difficulty. (Mostly due to language barrier). I'll probably consider the new save once / if a translation were to pop up. Best of luck on 19, my friend.