The elves need help, but they aren't ready to concede anything.
Souma a total coward did not lift a finger to protect his allies and political family in the conquest of the East Union conquest. Instead of being the protagonist of this light novel, he dedicates his time to making more offspring and giving a lot of excuses to his "allies".
The author insists on making this light novel about germs and disease. Thus the Elf Spirit Kingdom and the forces of the newly formed TIger Kingdom fall from the Demon Lord's territory plague. They call it the Spirit King curse that only "infects" warriors. Of course Souma could never get infected because he will never be a warrior. Nor is he a doctor, nor is the author or the illustrator doctors....hey wait, then why is Volume 15 about germs? Why is the Friedonia Kingdom worried about "solving" and "curing" a plague that is killing the elves and the soldiers of Haan (Tiger Kingdom)? Has Souma become so servile to Fuuga Haan and the elves, that now he is trying to cure those people? I think the first thing the author urgently needs to do, is get souma to wear one of Carla's maid outfits. Then Souma can abdicate and become Fuuga Haan's personal slave/maid.
If Souma and Friedonia have nothing to gain from helping out the elves, then why are they going to discover the cure to the plague? It is a contradiction to have the main character of a light novel, lose his protagonist status to Fuuga Haan. Fuuga Haan is the hero this series needs and yet, the Grand Chaos Empire does nothing, interferes in nothing. This is completely illogical, nonsensical and senseless.
The only positive thing is that this is the last volume so far. It is no longer about the Friedonia Kingdom, nor is Souma the main character of this light novel. Nor is it about governance or defeating the Demon Lord and recovering the lost territories. I see no future to this light novel.
The most likely outcome is that the Demon Lord is an older summoned Japanese person that got sick of this alternate world and now tries to destroy it. What would be the point of a series like this one? Or maybe the demon lord is a reader that had to go through all of this light novel and as revenge wants everybody to die (especially the warriors)?