Hoping this might help some. I have not had my P3A long, but from day one I have had Go App 1.3.20, FW 2.0.0 then 2.0.2 running on a Galaxy S6 with Android 5.1.1. I experienced what seems to be the common lag and freezing making video and any sort of FPV flight impossible. After several minutes of flight lag would start and eventually turn into a frozen screen that might update after 20+seconds. Also, my phone was always very hot after flight.
I read everything I could on the net and started to think the only cure was going to be to switch to an
Air 2 which, for many reasons, I did not want to do. The good news is my S6 is now working great and there is no IOS device in my future

(I do have what will be a dedicated Android Tablet in route as was my plan all along)
Another couple of notes on conditions.... My S6 resides in a thick heavy silicone and hard plastic case, I am sure this contributes to heat, but I am not willing to risk my phone falling unprotected. Also, all of my flights have been while temperatures were from the mid 80's to upper 90's in outdoor temperatures. I do try to stand in the shade for my comfort, but not always.
In short here is what I have done with my device and if it worked for me or not.
1. Use the close all function... didn't improve results...Still part of my preflight setup.
2. Airplane Mode... didn't improve results...Still part of my preflight setup.
3. Tried using a couple of App killers.... didn't improve results.... NO LONGER part of my preflight setup.
4. Changed from automatic channel selection to manual (channel 20) and turned bit rate to minimum....Did this at the same time as #5 see results there.... ... didn't improve results...Still part of my preflight setup.
5. Turned off video caching to my device....Saw some improvement ie. longer time before lag and freeze ups occurred but still far from what I think is usable...... didn't improve results...Still part of my preflight setup.
6. Downgraded Google Play Services to Version 7.5.71....didn't notice any real change.
7. Disabled Google Play Services....
THIS CURED THE PROBLEM!! I am now able to fly as long as I want, record as much video as I want, and I have noticed no lag, no freeze ups, and my phone is somewhere between cool and mildly warm after multiple batteries. (Before my phone was so hot after one battery I wouldn't have even considered more than one).
As for the disabling in #7 above, it was the only option left after the downgrade in #6. When I got into the Google Play Services portion of my application it indicates I still have version 7.5.71 and the only options are to "Force Stop" or "enable" it. I clicked "disable" to get it to this state.
As you can gather from the above items that I still go through I have not gone back to change settings and turn things back on to see if still having them adjusted this way is helping or not. My approach is that it is working so for the next couple of days until my tablet gets here I am leaving it alone!
This may or may not work for others, but after all of the valuable information I have gained here I wanted to try and give back something that might help others.