zephyr: Decrease update frequency of sync-public-streams.

zulip/integrations/zephyr/sync-public-streams

@@ -60,7 +60,14 @@ if __name__ == "__main__":
     zulip_client = zulip.Client(client="ZulipSyncPublicStreamsBot/0.1")
 
     while True:
-        time.sleep(15)
+        # Sync every 5 minutes because this makes a very large network
+        # request, due to Zephyr users who subscribe to 10K+ class
+        # names generated by a script.
+        #
+        # This delay means we won't subscribe to new Zephyr classes
+        # until 5 minutes after they are created in Zulip; this isn't
+        # great but an acceptable tradeoff.
+        time.sleep(300)
         public_streams = fetch_public_streams()
         if public_streams is None:
             continue