Hangs/becomes unresponsive when importing larger folders

[frozenpandaman]

When trying to import multi-volume manga/folders with multiple subfolders (e.g. 10 volume manga, each subfolder/volume with ~200 pages) the program just hangs on this screen with the cursor as the spinny beach ball of death.

Folders around ~500 MB work. Any above 800 MB seem to hang forever like this. Eventually shows "not responding" and requires a force quit. Running on El Capitan.

Also, unrelated, but navigation via up/down instead of just left/right would be great. Thanks!