Which trip had the shortest duration and started at the station that can hold 15 bikes?
shortest duration refers to MIN(duration); started at the station refers to start_station_name; can hold 15 bikes refers to dock_count = 15;
SELECT T1.id FROM trip AS T1 INNER JOIN station AS T2 ON T2.name = T1.start_station_name WHERE T2.dock_count = 15 AND T1.duration = ( SELECT MIN(T1.duration) FROM trip AS T1 LEFT JOIN station AS T2 ON T2.name = T1.start_station_name WHERE T2.dock_count = 15 )