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 Bahrain GP2 Series round"): It was the first round of the 2015 GP2 Series and was run in support of the 2015 Bahrain Grand Prix.
Relevant evidence: No