Hi!
I checked my gps.conf and everything seems alright. But i never got a faster fix than 15 seconds(normaly around 30-60 seconds) on the x10iii.
Grapheneos has its own supl proxy, which can be used by non grapheneos users too.
I changed the AGPS part of my gps.conf to these settings
# FOR SUPL SUPPORT, set the following
SUPL_VER=0x20000
#SUPL_HOST=supl.google.com
SUPL_HOST=supl.grapheneos.org
SUPL_PORT=7275
(Yes it is port 7275)
and did some tests.
OUTSIDE 1st test: 3 sec until fix
OUTSIDE 2nd test 2 sec until fix
OUTSIDE 3rd test 5 sec until fix
INSIDE 10 sec until fix.
I did a reboot between every test, so the graphene os proxy seems to work for me.