Yes, that is the right file.
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
would become
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash video=eDP1:1920x1080-16"
My output of xrandr | head
Screen 0: minimum 8 x 8, current 1920 x 1080, maximum 32767 x 32767
eDP1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 340mm x 190mm
1920x1080 60.01*+ 59.93
1680x1050 59.88
1400x1050 59.98
1600x900 60.00 59.95 59.82
1280x1024 60.02
1400x900 59.96 59.88
1280x960 60.00
1368x768 60.00 59.88 59.85
I have other optimizations also, which might be contributing to the +ve effect. If so, mine is:
GRUB_CMDLINE_LINUX_DEFAULT="quiet norandmaps nokaslr audit=0 cgroups_disable=memory video=eDP1:1920x1080-16"