Extremely slow library update?

Hello all, just wondering if this is normal / expected behaviour or if something is wrong.

I am currently running Kodi 16.1 on a Raspberry Pi 2 via RetroPie. I just added two TV series, both with ~20 episodes at ~8 seasons so I guess about 320 episodes total, .avi format. I told Kodi to “update library”, like, two hours ago and I’m still sitting here watching it slowly chug through the second series. Should library updates take this long? Is it because of the RPi or because I’m running Kodi via RetroPie, or is this just normal? The files are stored on an external 3TB HDD which has its own power supply, plugged directly into the Pi via USB 3.0.

Thanks!