Hi. First I have to say I am a novice, so take this for what its worth.

I plugged the url into a loop and just started messing with a D scale. Seemed to fit to my ears. The piece, which is beautiful btw, seems expressive to my ears. So what I am saying is that when I played over it, I stayed within D and kind of felt my way along, meaning I didn't stick to a rigid bpm.

Hope this helps.