An average m3u of 2-3mb size loads in 10-20 seconds, while a 23mb m3u that I have takes 1 min and then its quite slow to browse on the app. So in general the list should load in a few seconds.

Tell him to download the m3u on a web browser and check does it work with VLC player, then input that url on siptv website or upload that working m3u to his MAC on same website.