Same issue here. Even docker -v consistently takes 17 seconds when my host Windows 10 laptop is connected to the network via Wifi. As soon as I disconnect from that wireless network, or turn-off Wifi, the operations are instant. Even the Tray Icon takes 15 seconds for the menu options to even come up. Same behavior for both Linux container or Windows container mode.
An example …
PS C:\dev> get-date;docker -v;get-date
Saturday, September 8, 2018 8:35:40 AM
Docker version 18.06.1-ce, build e68fc7a
Saturday, September 8, 2018 8:35:56 AM
RESOLVED
This posting on github pointed me to the solution. As noted above, I originally thought it was due to me being on wireless because the commands would execute quickly when I disconnected wireless. I finally had a chance to connect to my ethernet from home and had the same problem.
After the github posting, I connected to corp via our VPN and the Docker commands then executed MUCH more quickly. There is still a minor one second-ish delay, probably due to latency of the domain controller calls, but that’s all.