Recommended versions updated

Author: CubeEngine Sponge Updater

recommended-versions.json

@@ -3,5 +3,7 @@
   "12": "1.21.1-12.0.3",
   "13": "1.21.3-13.0.0",
   "14": "1.21.4-14.0.0",
+  "15": "1.21.5-15.0.0",
+  "16": "1.21.8-16.0.0",
   "8": "1.16.5-8.2.0"
 }