Could you send SELECT * FROM pg_config()
and try to find the CPU model ?
I think it's possible the hypervisor is trapping and emulating unhandled CPU
instructions.
Actually, it would be interesting to see if the performance differs between
11.2 and 11.13. It's possible that EDB compiled 11.13 on a newer CPU (or a
newer compiler) than 11.2 was compiled.
If you test that, it should be on a separate VM, unless the existing data dir
can be restored from backup. Once you've started a cluster with updated
binaries, you should avoid downgrading the binaries.