Many thanks Rudy
Glad to help!
One additional thing. If you have 15 Gb of sheet music, that must be quite a number of songs.
If you are considering loading all that in Mobilesheets and adding some metadata to it (artist, composer, key, album . . . . ), you may want to check out the PC Companion of Mobilesheets.
It is free software for windows pc's, and works as a sort of remote control for mobilesheets.
The principle is as follows.
You need a tablet with mobilesheets and a windows pc with PC companion installed.
Both have to be on the same network.
You launch the PC companion on the pc
You launch Mobilesheets on the tablet, and in the overlfow menu you select 'sync to PC'
Mobilesheets will then connect to the companion, and from there on you can work in Mobilesheets using your PC.
Whatever you enter or change in PC companion on the PC is not stored on the PC, but transferred realtime to Mobilesheets on the tablet.
You can batch import music scheets using the companion, they will all be sent to the tablet.
You can also make a backup of all your sheets including annotations, metadata . . . using the companion. That backup file can then be stored anywhere you have access to from your pc (it may take awhile for 15 Gb as it will all be transferred from the tablet to the pc . . .)