sudo mkdir -p /usr/share/keyrings

curl -fsSL https://www.postgresql.org/media/keys/ACCC4CF8.asc \
| sudo gpg --dearmor -o /usr/share/keyrings/postgresql-archive.gpg

UBUNTU_CODENAME="$(lsb_release -cs)"

sudo tee /etc/apt/sources.list.d/pgdg-archive.sources > /dev/null <<EOF
Types: deb
URIs: https://apt-archive.postgresql.org/pub/repos/apt
Suites: ${UBUNTU_CODENAME}-pgdg-archive
Components: main
Signed-By: /usr/share/keyrings/postgresql-archive.gpg
EOF

sudo apt update

apt-cache madison postgresql-15 | grep 15.6
apt-cache madison postgresql-client-15 | grep 15.6 

root@playground /e/a/sources.list.d# apt-cache madison postgresql-15 | grep 15.6
postgresql-15 | 15.6-1.pgdg130+1 | https://apt-archive.postgresql.org/pub/repos/apt trixie-pgdg-archive/main amd64 Packages

root@playground /e/a/sources.list.d# apt-cache madison postgresql-client-15 | grep 15.6
postgresql-client-15 | 15.6-1.pgdg130+1 | https://apt-archive.postgresql.org/pub/repos/apt trixie-pgdg-archive/main amd64 Packages

sudo apt install -y \
  postgresql-15=15.6-1.pgdg22.04+1 \
  postgresql-client-15=15.6-1.pgdg22.04+1