The same Ibn Fadlan also clearly differentiated between the Turkic peoples he met on his way and the Volga Bulgars themselves. As I said, a few word excerpts don’t make a language. Especially in an ethnically diverse area as that of medieval Volga Bulgaria (and you conveniently forgot to mention a whole bunch of other tribes in that area).
As for the “If they were Iranic, they would have left a legacy” argument – well, if they were Turkic, where’s their legacy in Danubian Bulgaria? Those 15 words? Or maybe the Kutrigur Bulgars were Turkic and the others were Iranic (actually, that’s not out of the question – the Kutrigurs had spent more time with the Huns and then the Avars, after all)?