domain name system - Google DNS is too slow connecting to Google APIs

I have a linux server in Germany. The server is configured with Google DNS. When I call from the server some Google API, the connection is too slow, it takes always 2 or 3 seconds to connect to the Google server. I have no problem connecting to other servers.
Paradoxically it seems there are problems resolving Google URLs with Google DNS.
I have temporarily resolved inserting a row in the file hosts.txt that associates the Google IP corresponding to the Google API that I use.
Can I resolve this problem in another (clean) way?
Thank you!