Are all these sourced in your Oreo folder available?
By he way, the builde.sh script isn’t working anymore on my side. And since all sources are available in e-git you can use this way too [HOWTO] build eOS in old fashioned way with breakfast -- now with interactive script
I prefer using this way.
Starting in OREO folder with
sudo su
source build/envsetup.sh
And I hope, your sources are really 15.1 sources, because the sources you have forked from are all 17.1 sources