Does “Coderus’ method” address this guide at TJC: [How-to] Make Aqua Fish to think it’s Jolla C [not modem]?
Note that you omitted SailfishOS 4.4.0, which is a stop-release (as all SailfishOS 4.x.0 releases; the point release number (i.e., fourth field) does not matter), as an intermediate step. One must not “jump over” any stop release; if you do, flaws must be expected, which are hard to impossible to resolve without resorting to re-flashing.
But AFAIU, with 4.3.0.12 all was working fine, but after upgrading to 4.3.0.15 the camera app started crashing and displaying a “test image” with colour bars and pixeled window. This is unexpected, as the changes between 4.3.0.12 and 4.3.0.15 were minimal and did not alter anything related to the camera app or the camera module (i.e., the camera hardware), for details see Changelog_from_4.3.0.12_to_4.3.0.15.md.
You seem to have observed some error message that /vendor/lib/egl/libGLESv2S3D_adresno.so is missing, correct? BTW, is the file-name absolutely correct, I wonder about the adresno? You may try to save it before the upgrade and restore it afterwards. This is best done on RPM level, so execute rpm -qf /vendor/lib/egl/libGLESv2S3D_adresno.so to determine which RPM package provided the library which is missing on 4.3.0.15; this has to be done, when everything is working fine, i.e., on 4.2.0.* and / or 4.3.0.12 (I would rather do it twice in different directories and check if the downloaded RPM files are really identical by diff -q <file_a> <file_b>, which outputs nothing if they are exactly the same). Then download that RPM file as root by pkcon download . <name_of_RPM-file>. Later (when the camera etc. are failing due to the missing so-file) you can install the downloaded RPM file by pkcon install-local <name_of_RPM-file>.
HTH!
P.S.: I do not comprehend, what you try to express with “→ /usr/bin/killall minimediaservice → sucks” and " GPS (gpsinfo, PureMaps, Maep) not working (same as camera lib missing)". Can you please elaborate these two statements a bit, the people may be able to provide better help.