Unable to upgrade to PostgreSQL 15/

[Ed_S]

@glorioustn

popen failure: Cannot allocate memory

This is perhaps the most serious - you need more RAM or you need to add swap.

Please post the output of these quick diagnostics:

@Ed_S

cat /etc/lsb-release
uptime
df -h /
free
swapon
vmstat 5 5
dmesg|egrep -i "memory|oom|kill"
ps auxrc