Take it back to the dealer and tell them. likely they won't find a fault, as it's intermittent. Ask them to install the latest software (59.00.502) and Music database (Gracenote 8 ). If they will do this for free, GREAT. If not, you can pay them to do it or come back here and we can talk you through the process (or you can easily read about it here also)
Before going back to the stealership, try and work out if there is any regular pattern or sequence or thing that sets off the slow boot?