I try to play as much of the 3 hrs as possible to maximize your tips,....15 minute breaks during dinner is way too long IMO...
I usually play 1 1/2 hrs straight, then take a 5 min break...
and then play the rest of the gig straight thru..... I sing 99% of my songs also.
For a 3 or 4 hr Dinner & Dance that's a different story.