feat(postgres): add PG 15.15

[hunleyd]

What kind of change does this PR introduce?

add PG 15.15 to our AMI

What is the current behavior?

no 15.15

What is the new behavior?

has 15.15

Additional context

https://www.postgresql.org/about/news/postgresql-181-177-1611-1515-1420-and-1323-released-3171/

[yvan-sraka]

What's making the check here fails is building a lot of pgrx-based extensions versions in parallel, that make the runner crash. As demonstrated here, without most of them the PR pass. This should be fixed by https://github.com/supabase/postgres/pull/1745