How many books do you have on the device? The import time goes up as the number of books does, but, from my experience, you would need a very large number of books before it got that bad.
A more likely reason is that the database on the device is corrupt. Depending on what part is corrupted, this will slow things down. You can test this with an SQLite management tool, or if you are a calibre user, my Kobo Utilities plugin can do it. Though, if you are a calibre user, you would probably get an error when it is getting a list of books from the device.
It could also be a failing internal Micro SD card (@JSWolf suggested). If it is, you can replace it and restore an image to the card. That will usually fix problems like this.
What I would suggest you do at this point is:
- Test the database.
- If the database is corrupt, do a sign-out of the Kobo account. Then do the setup again. This will rebuild the database and import the books again.
- If that doesn't help, do a factory reset. This will restore the device to as-new configuration and you an go through the setup again. You will lose all sideloaded books.
- If it still fails, replace the SD card. I can supply an image for your device to do this.