You don't need all the delays... probably only one after the
AT+CMGS=\"+6xxxxxxxxxx\"\r"
command... this is to allow the modem to respond with a prompt, so you can then send the message... probably only 100ms or so will do.
These commands only need to be issued once, so you can put them in your setup
"AT+CMGF=1"
"AT+CNMI=2,2,0,0,0"