I have verified 1.5+18.10ubuntu1 as working on my cosmic system. I was using it all the time to build classic images and everything worked as expected.
I also performed one test build of a model-assertion-based image:
$ ubuntu-image snap -d -O out test.model
(...)
$ cd out
$ ls
pc.img seed.manifest snaps.manifest
I have verified 1.5+18.10ubuntu1 as working on my cosmic system. I was using it all the time to build classic images and everything worked as expected.
I also performed one test build of a model-assertion -based image:
$ ubuntu-image snap -d -O out test.model
(...)
$ cd out
$ ls
pc.img seed.manifest snaps.manifest
The pc.img image boots correctly.