Have you checked if Postgres works via the py-postgresql driver? It's implemented in only Python 3, with all C optimisations optional.
https://github.com/jkehler/awslambda-psycopg2
https://www.reddit.com/r/aws/comments/3on09a/using_psycopg2_...
https://forums.aws.amazon.com/thread.jspa?messageID=680192
Have you checked if Postgres works via the py-postgresql driver? It's implemented in only Python 3, with all C optimisations optional.