Bug 566640 - Add support for Linux AArch64

Change the justj.jregen model to use Java 15 manifests by default.
diff --git a/model/org.eclipse.justj.model/justj.jregen b/model/org.eclipse.justj.model/justj.jregen
index 5f9a398..14570d2 100644
--- a/model/org.eclipse.justj.model/justj.jregen
+++ b/model/org.eclipse.justj.model/justj.jregen
@@ -8,7 +8,7 @@
     provider="Eclipse JustJ"
     providerImageName="justj32.png"
     target="jre-gen"
-    source="https://download.eclipse.org/justj/jres/14/downloads/latest/justj.manifest"
+    source="https://download.eclipse.org/justj/jres/15/downloads/latest/justj.manifest"
     localCache="local-cache">
   <touchpoints
       phase="uninstall">