New "App" version can't handle large files.

[daviesj]

New version (XstReader.App.2.1.1) is unbearably slow when reading large files. 1.5GB file took about 20 min to load and is quite slow in switching between messages/folders). In comparison, "old" version (XstReader.v.1.15.0) loads the same size file in about a second and switches much more quickly between folders & messages.

[ldx63]

I confirm the same behaviour.
Unfortunately, it seems that 1.15 doesn't correctly handle UTF-8 encoding, otherwise it would be good for a basic functionality.