Recently Google revealed new Android M with many features and one of the feature include : External memory can be used and Internal memory .
This feature will be of great use for the Devices which comes with Low internal memory . If your device will be up gradable to Android M then your Storage Running out problem will be solved by just interesting an external Sdcard .
|Pic credits - AndroidPolice|
By this feature your External memory will act as Internal and vice versa . Every app data will be saved at External memory .
This is a great feature , the thing required is Android M on your device .