15% of 25 minutes is roughly 3.75 minutes on a good battery... Auto-landing initiates immediately and begins a slow decent wherever it currently is. So when you hear your first warning at 20% or 30% consider flying back closer to HOME.
Assuming you have 3.75 minutes at 50% max throttle & velocity (50% of 35moh = 17.5mph) and .75 of those minutes would be used for your descent, 3 minutes at 17.5mph covers 4260 feet (1408 meters) distance back to HOME under "ideal" (calm) conditions. You will burn considerably more reserves fighting wind & turbulence.
So, in most cases (unless your me, Uncle Fester, BendronePilot, themosttoys, and a few other long-distance fliers) you'll probably have enough juice to get home & land safely, particularly if you heed the first warning and fly closer to home and maintain LOS (line-of-sight).
If it initiates an auto-landing, throttle up a bit to gain enough altitude to clear people & obstacles and bring Vision in towards you... Use the Radar display if you're having trouble with orientation & distance or difficulty seeing the aircraft. Try not to "floor the sticks" else you risk dumping the remaining charge in the battery.
Hope that helps!
iDrone