Low performance between datacenters

hi All,

I am new on the list.
I hope someone can give me an adequate answer or good advice about my
problem.

I have a client (normally a web service, for testing the psql client) in
GCP. There is a PSQL server in another DC. The ping response time is 20ms.
I measured the bandwidth via scp and it is more than 1Gb/s which is more
than enough IMO.

The psql connection between the DCs for me was unexpectedly slow.
I would expect a bit slower query without data ('select now()') due to the
increased latency and somewhat similar speed of data transfer.
What I see is that

select now() increased from 0.7ms to 20ms which is OK.
And 'select *' on a table with 3082 rows (so it's a small table) increased
from 10ms to 800ms.

Is this normal? Can I improve it somehow?

Thank you,