Question: How many teams were represented in the pair of motor races held on 18 and 19 April 2015 at the Bahrain International Circuit in Sakhir, Bahrain?
Sentence (from "2015 GP2 Series"): The 2015 GP2 Series season was the eleventh GP2 Series season, a championship for open-wheel racing cars run as a support series to the 2015 Formula One World Championship.
Relevant evidence: No