I would think that is best answered by SoundCloud. Way too many variables for me to guesstimate an answer.
Curiously I can not find a Contact point on SoundCloud, but I'm not a member.
You could try their forums:
https://www.soundcloudcommunity.com/soundcloud Maybe users have a good guess.
I would state that anything someone tells you is an estimate, there is probably no way for them to give an exact number as they can't match your particulars: device + cellular service (including how towers are running at this moment for you) + unique stream request.
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