If you're done with the research, I think your best bet is to complete Adv. Scouts for Ch. 15 so that all the Ch. 14 quests become declinable.
I'm not sure exactly which quest you're stuck on, but it looks like there are 4 possibilities:
Collect 100 humanium and 100 elvarium - reward: 10000 elvenarin
Collect 400 humanium and 400 elvarium - reward: 20000 elvenarin
Gain 20 relics and 500 elvarium - reward: 200 humanium
Gain 2000000 supplies and 500 humanium - reward 200 elvarium
None of those quest rewards are of any use to you if you're done with the research so you don't lose anything useful by declining them.