Guys... Tablet has a 6000 mAh battery. If it starts from 0% (dead device) battery is charged very slow for a while, then speed increases and about 90% (moment, when LED turns green) it slows down due to specific of Li-Ion battery.
Supplied wall charger has 1500 mAh power output. Doing simple math means 4 hours and some minutes is a bare minimum. When device is on (screen off) some power goes to device, there is also some energy loss during charge process itself. I think up to 5 hours for Z2 tablet with fully discharged battery is near to normal.
Also try to avoid discharging the device below 10-20%. This way you can extend battery lifespan
