What are the new features of keycloak-15.0.2 over older versions.?
https://www.keycloak.org/docs/latest/release_notes/index.html
Usually, in patch versions there are no real new features.
Before upgrading I recommend your carefully review the open and closed ‘issues’ in pending release 16.0.0. There are a few critical issues in 15.x which may or may not impact you. Specific examples include MSSQL and use of SAML SP/RP with SAML IDP:
https://issues.redhat.com/projects/KEYCLOAK/versions/12359439