So my questions is it possible that my app engine instance are lacking of some resources or smth? Maybe I am lacking of some configuration or JAVA OPTIONS, because now I use default. Maybe someone has faced similar permormance issues.
Update. Again I have tried to use B1 B2 B3 B4 instances. Same results. Feels like the applications has really small amount of resources.
Problem solved, when I created Compute Engine VM. In virtual machine I have running docker image with the same application. And now it works fine. Responses are great.
I would love to use App Engine, but still cannot figure out what causes this. I use all default settings of app.yaml from google tutorials with no additional options.