xperia z4 tablet why is android system showing 9.79 gig

[bikepack]

i have a relatively new z4 tablet and in checking internal storage i found that android system is taking up almost 10 gig of space. i believe that the tablet shipped with lollipop and is now running nougat. I seems to me the 10 gig size is inappropriate- correct? If so how do i find the cause? Do i need to root?