It's one of the limitation with 16gb internal storage devices today...
The only solution is to root your phone and use 3rd party apps like Foldermount to move app data to external micro sd card..
There is xda forums on how to root your phone without unlocking bootloader.
Always do a full backup before attempting these incase something goes wrong... Only do rooting if you are aware on how to do it.
Rooting might break banking applications or banking applications might not work when root is detected . Also tap and pay via NFC might not work if rooting is done.
Otherwise it's fine to do it.... foldermount app is the only easiest way to solve storage space issues
