I tested Google Home along with Alexa and Homekit….forget Homekit. As for Google Home, I found that if I changed my router settings to use the Google DNS instead of my ISP...Telstra....then Google Home responded quicker across the board.
I kept the same set up for Alexa and it made little difference because Alexa was almost instant in response times.
Google
Public
DNS
operates recursive name
servers
for public use at the IP
addresses
8.8.8.8 and 8.8.4.4 for IPv4 service
I am currently testing the Cloudflare public DNS which is said to be faster again.
Cloudflare is 1.1.1.1 and 1.0.0.1