You can’t mix and match arbitrary versions of the web vault and backend server. Upstream Bitwarden rolls out compatible releases concurrently, and bitwarden_rs does this via the Docker images. If you want to handle builds yourself, then you need to handle the version matching yourself.
If your main goal is to run without Docker, probably one of the easier ways is to extract the /bitwarden_rs binary and /web-vault from bitwardenrs/server:alpine.
If i follow @BlackDex’s advice, at this line, I grab the hash a6705a4d7776500a6544afd141de1786e6b87c386b068be996294960779cb5bf, this hash is linked to this image, so the version 2.16.0b and not 2.15.1 as @BlackDex says… Am I wrong?