--- Comment #12 from Michael Chang email@example.com --- (In reply to Jan Matejek from comment #11)
(In reply to Michael Chang from comment #10)
BUT, there is still roughly the same delay before the image appears
How the delay was measured? Is it still gfxterm (no theme enabled) with backgroud image that could reproduce it? How about the disable the background image completely and leave on gfxterm or do not scale the background image by changing, for eg.
background_image -m stretch /boot/grub2/themes/SLE/back-640-480.png to background_image -m normal /boot/grub2/themes/SLE/back-640-480.png
in /boot/grub2/grub.cfg ?