Navigation from sub folder to root folder - slow loading time

[masterjp]

My android tablet (android 16) can handle micro sd cards.
I have a big collection of pictures (up to 3000x2000 pixels) up to 100.000 pictures in different sub folders (around 100 folders) in a root directory.
The whole picture collection is completely scanned by xnview mobile.

If I switch from root directory to a sub folder, the performance is okay compared with the amount of pictures and thumbnail size and amount.
If I go back from sub folder to root folder, the loading time will be very long.

Other gallery apps are faster or use a second cache for thumbnails or folder informations.
Is it possible to boost up the navigation of folders?
It is okay, if xnview mobile show the folder thumbnail grid and folder names first.
In a second step it could load and show the thumbnail pictures.