Steps to reproduce:

1. Open the attached project.
2. Go to build settings and set it to Android platform and 'Texture Compression' set to ETC2.
3. Go to 'Preferences' and make sure 'Compress Assets on Import' is turned on.
4. Go to 'DeNA' in the menu bar and select 'Asset Batcher'.
5. Set everything up just like in the attached image and press 'Batch Texture Settings'.

It takes an incredibly long time to re-import one texture (it took 192 seconds). And the user is using a custom script.

Reproduced on: 5.4.0p1, 5.4.0f3, 5.3.6f1.