Add compatibility for Postgres 15

[0xJchen]

Hi Chris, thanks for sharing this great project! I met some problems when running it and hope the following solution would help others.

The default Postgres version here will be 15, and we will need to grant scheme public to new users as specified here.

Also on the second post, there is a typo: all theoreticalOptionalValue should be theoreticalOptionValue to adapt to the codes mentioned. Though this problem does not appear in the codebase.