Token generation using email and password really slow

I use my own dotnet backend service as a proxy to the auth API.
When I generate access token using email and password API returns response after long period of time (3-12 seconds). I understand that it cannot be super fast (like 100ms) but everything above 5sec is too long.
I already tried tricks like using connection pool for http client, heating it up in background worker.
Backend runs in the k8s cluster (GCP Warsaw) but it is slow on my local machine also.

I have tried to generate access token in the chron job recently, so maybe I’ve throttled