I'd go with develop. Development ties up character/s for that turn, correct? So if we develop now, we can finish it up next turn with less characters than it would otherwise take, so we have more people available to crack heads with. I assume the 15 Res was the 1st upgrade, so 16/??? for the next one then?
I assume chatting doesn't take up anyone's action/turn? Depends somewhat on how large a portion of the next upgrade our Res would yeild us, and how significant a boost chatting gives. How wold chatting compare to equipment/stat pills?
Anything >50% would probably be worth it. But thats just me, i overanalyze for fun