Put the following into /etc/X11/xorg.conf.d/00-keyboard.conf
# Written by systemd-localed(8), read by systemd-localed and Xorg. It's
# probably wise not to edit this file manually. Use localectl(1) to
# instruct systemd-localed to update it.
Section "InputClass"
Identifier "system-keyboard"
MatchIsKeyboard "on"
Option "XkbLayout" "us"
Option "XkbOptions" "caps:escape"
EndSection
Other xkb options are listed in the file /usr/X11/xkb/rules/base (openSUSE Leap 15.1), such as caps:swapescape which swaps escape and caps instead.