I downloaded the upgrade script

curl -s https://upgrade.odoo.com/upgrade > upgrade.py

modified the script

from 

def get_db_contract(dbname):
    try:
        output = subprocess.check_output(
            [
                "psql",
                dbname,

To

def get_db_contract(dbname):
    try:
        output = subprocess.check_output(
            [
                "psql",
                "-h",
                "",
                "-U",
                "",
                dbname,

do the same for pgdump and pg_restore and createdb lines/code

trusted all connections to postgresql by editing pg_hba.conf

installed openssh-client , and rsync

execute the script as

python3 < (cat upgrade.py) test -d <dbname> -t 15.0