You can't set a 2015 Leaf for 80% charge, I'm afraid. That ended in 2014. You have to just estimate when it will reach that point, and unplug it then.
The best strategy would probably be to charge to about 70% for the short trips, doing it every other day if that works out ok, and then charge to 100% right before the longer trips, letting the pack equalize but not letting it sit long at 100% indicated charge.
2013 "Brilliant Silver" SV with Premium Package and no QC, and 2009 Vectrix VX-1 with 18 Leaf cells.
The most offensive, tasteless phrase in use here is "Pulled the trigger." I no longer respond to posts that use it.