I just finished 4 AAU games under the exact conditions you said (70-75 min intervals, 16 min halves). I feel it's best to switch on almost every shooting foul no matter how tired you are b/c you don't have to run during this time. It takes a little time for everyone to get set up for the free throw so you don't have to run on these switches. If you don't switch then the lead has to come around the players, report the foul, get everyone set and administer the FTs while the Trail is left picking his nose. The only time I don't switch on shooting fouls is when I or my partner is lagging behind in transition and they have to come a ways down.
I tell you though we sure were tired of switching after the 3rd game (60 combined fouls, fire alarm for 30 mins, 2 T's on head coach, 1 T on Asst Coach, and an elephant ran on the court which took awhile to clean up the mess it left
). The game took 2 hrs instead of the 70-75 mins. To top it off the same team played in the next game (my 4th)!