Is it possible to build docker images using docker-compose concurrently?
Yes, it's possible. You can use --parallel option since docker-composer 1.23.2 version.

Version 1.23.2 also correct 1.23.0 bug: 


  Reverted a 1.23.0 change that appended random strings to container
  names created by docker-compose up, causing addressability issues.
  Note: Containers created by docker-compose run will continue to use
  randomly generated names to avoid collisions during parallel runs.


https://github.com/docker/compose/releases/tag/1.23.2

You can use it simply doing:

docker-compose build --parallel