Comment # 11 on bug 1123228 from Terje J. Hanssen

Yes, this issue still occure on Leap 15.1 on Dell XPS 13 with HiDPI.

The (Grub2) boot menu from the USB installation media is too small with small
and almost unreadable fonts.

Coming further to the yast2 graphical installer with the language and keyboard
selection and the license agreement, the fonts are quite fine.

Also after installation, the Grub2 triple-boot menu in my case

openSUSE Leap 15.1
Ubuntu 18.04.2 LTS
Tumbleweed

is too small with small and almost unreadable fonts.