Is there a trick to make the battery last longer during the flight . Fly slower or ... ? I have phantom 3 adv. Thanks advanced

How much time are you getting from your battery? Flying conditions will drive different results. I.e., cold vs hot, windy vs not windy, lots of altitude gain, etc.

typically flying in Atti mode will yield a higher battery time as it wont fight winds to keep position.

If you spend time trying to extend flight time, I think the seconds you may gain will interfere with the joy of flying how you want to fly.

I need to fly not for joy I am recording some commercial film.