@ Coxco - On my complete stock DJI F450 with NazaM Lite & GPS use the stock 8x4.5 slow flyer props and a 3S5000mah 35C-50C lipo I get OVER 15 minutes of agressive flying around 20+ just hovering and slow flying.
Did you calibration the NazaM Voltage sensor and also did you set up the First and Second Level Low Voltage Warnings properly??? Did you also set the right Line Loss Value for your batts you are using?