I don't think this is possible or realistic, but according to this article you can try installing GApps on top of MicroG-build. Of course that would mean losing all benefits of having MicroG, but since you don't care for MicroG it should not bother you. If it does not work, you can always revert to the last backup you've made.
---------- Post added at 03:04 PM ---------- Previous post was at 02:25 PM ----------
GOOD NEWS! At last, I found the final LOS 15.1 build for OP2!
lineage-15.1-20200223-nightly-oneplus2-signed.zip
/!\ REMINDER: You should always check the SHA signatures for any build you download from an unofficial source!
According to lineageoslog.com SHA-signatures are:
Please note, that lineageoslog.com is not run by and not affiliated with LineageOS-team in any way. It is not an official website.
But if you perform a literal search for the build number or SHA-1 signature on Google, you can find cached results referencing to official lineageos.org download page.
Since the signatures seem legit and they match the file checksum, I judge it safe to say that the build linked above is the official final version of LOS 15.1 for OP2 (as of 2020-08-13). But don't take my (or anyone's) word for it, always check SHA signatures yourself!
IT'S A SHAME THAT LINEAGEOS.ORG DOES NOT LIST SHA-SIGNATURES FOR OLD BUILDS ON THEIR OFFICIAL WEBSITE!