release prepare for 3.15 - updating build.xml and status.xml

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1761161 13f79535-47bb-0310-9956-ffa450edef68

build.xml

@@ -40,7 +40,7 @@ under the License.
 
     <description>The Apache POI project Ant build.</description>
 
-    <property name="version.id" value="3.16-beta1"/>
+    <property name="version.id" value="3.15"/>
     <property name="release.rc" value="RC1"/>
 
     <property environment="env"/>