Windows 10 slow boot after driver installs
When you want to install graphics drivers and other drivers in the image in superclient mode, it boots slower.
When you have client set in superclient mode to install drivers, it will not use the client cache to cache files that are loaded during booting. hence the boot speed is longer (slower). And when you reboot the client after installing drivers, the data is being sent to the server so its slow to boot.
Once you have finished installing drivers, disable the superclient and then save the image. Once the data has saved, boot the client once normally, it will be slow at first, then reboot the client and it will boot faster as the image data is cached on the server. First boot on any diskless system is slower than the subsequent boots.
Also, make sure that you have "Enabled Client Cache" check and set, client cache helps in boot up of clients.