Endgame really needs balancing. Counquring last territory, i'm still not even close to buying medicine, and i'm still lacking last two achievements in gold :/
Sudden percentage drop around 15k is not a bug, it's a feature. This is the moment when game gets badges, and a whole wave of haters come by and rate it down.
The prize giveth, and the prize taketh away. Thanks for letting me know, I'll try to post a fix for that this evening.