TLP made any improvement out of the box and the configuration is for geeks even with the GUI 
I installed « auto-cpufreq » (from snap) and things improved dramatically from 4-5h to more than 10h not far from the hardware benchmark.
Snap however does not allow to run the GUI and the post-install disabling GNOME power profile.
I hope for a Zorin deb package of auto-cpufreq