This usually depends on your internet speed or the server load of the IPTV provider, not the .m3u file itself.
To watch the channels contained in the 0021-tv_channels_dragon123_plus.m3u file, you need an that supports .m3u formats.
(Android) Import the file via the settings menu. Kodi: Use the "IPTV Simple Client" add-on.
If the links in the file are old, the stream might be broken. IPTV links expire frequently.