chore(deps): update dependency com.google.protobuf:protobuf-java to v3.15.0

Author: renovate-bot

pom.xml

@@ -578,7 +578,7 @@
     <project.jsr305.version>3.0.2</project.jsr305.version>
     <project.gson.version>2.8.6</project.gson.version>
     <project.jackson-core2.version>2.12.1</project.jackson-core2.version>
-    <project.protobuf-java.version>3.14.0</project.protobuf-java.version>
+    <project.protobuf-java.version>3.15.0</project.protobuf-java.version>
     <project.guava.version>30.1-android</project.guava.version>
     <project.xpp3.version>1.1.4c</project.xpp3.version>
     <project.httpclient.version>4.5.13</project.httpclient.version>