Advice on tipping for caterers and staff?

Hi so my wedding is coming up and we hired Lucille's bbq for our catering. They are only doing delivery and not doing any type of set up. Would we still need to tip the usual 15% of our bill just for delivery? Also, our venue charged us a mandatory service fee and also included the gratuity in the invoice. Would we still need to tip the staff again on the day of the wedding or was that the gratuity that we already paid for? Please help! Thank you