Increased after send delay

app/src/main/java/eu/faircode/email/Core.java

@@ -118,7 +118,7 @@ import static javax.mail.Folder.READ_WRITE;
 
 class Core {
     private static final int MAX_NOTIFICATION_COUNT = 100; // per group
-    private static final long AFTER_SEND_DELAY = 10 * 1000L; // milliseconds
+    private static final long AFTER_SEND_DELAY = 15 * 1000L; // milliseconds
     private static final int SYNC_CHUNCK_SIZE = 200;
     private static final int SYNC_BATCH_SIZE = 20;
     private static final int DOWNLOAD_BATCH_SIZE = 20;