Question: In 2015, what percentage of trips that had the subscription type was Customer and ended on a rainy day?
SQL: SELECT CAST(SUM(CASE WHEN T2.events = 'Rain' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(T1.id) FROM trip AS T1 INNER JOIN weather AS T2 ON T2.zip_code = T1.zip_code WHERE SUBSTR(CAST(T2.date AS TEXT), -4) = '2015' AND T1.subscription_type = 'Customer'