Does MKV streaming need to read all tracks or just the ones playing?

[pintassilgo]

Example: I have a 18.6GB MKV file. Video is 12.8GB, lossy audio is 1.10GB (there is a lossless 4.11GB track too) and the subtitle I want is 21MB (there are dozens of subtitles in the file).

To know if my internet speed is enough to stream this video, should I consider 18.6GB (the entire file size) or just 13.9GB (sum of tracks I'll need)?

If it's the entire file, I'll remove all needless subtitles and the lossless audio track.