I have been dealing with this since changing to the WIE for driver and secure boot support.
WinPE is larger etc, and TFTP is slow. Today I decided to really look into this, and the advancement of AI really helped me narrow down what I could do.
in short I started using OpenTFTP server, and set it's default home folder to C:\Program Files\Theopenem\tftpboot\, then configured the block size to it's max, 65464. After that I used Bootice to modify the BCD file in the C:\Program Files\Theopenem\tftpboot\boot, adding elements:
ramdisktftpblocksize = 65464
ramdisktftpwindowsize = 8
now instead of 2:30 for it to boot it's about 25 seconds. You can also make some improvement to speed without changing the TFTP server just by modifying the BCD, you might also need to update the TFTP32 INI, I added
MaxBlockSize=65464
and set WinSize=8
It was faster, but OpenTFTP server was even faster.
I really hope this helps someone!