เมืองที่มีอย่างน้อย 15 สถานีมีชื่อเมืองอะไร และมีกี่สถานี แสดงสัดส่วน ไม่จำเป็นต้องใช้ทุกตาราง
What is the name of every city that has at least 15 stations and how many stations does it have. Show the proportion.It is not neccessary to use all the tables.
 weather:  date [ TEXT]  max_temperature_f [ INTEGER]  mean_temperature_f [ INTEGER]  min_temperature_f [ INTEGER]  max_dew_point_f [ INTEGER]  mean_dew_point_f [ INTEGER]  min_dew_point_f [ INTEGER]  max_humidity [ INTEGER]  mean_humidity [ INTEGER]  min_humidity [ INTEGER]  max_sea_level_pressure_inches [ NUMERIC]  mean_sea_level_pressure_inches [ NUMERIC]  min_sea_level_pressure_inches [ NUMERIC]  max_visibility_miles [ INTEGER]  mean_visibility_miles [ INTEGER]  min_visibility_miles [ INTEGER]  max_wind_Speed_mph [ INTEGER]  mean_wind_speed_mph [ INTEGER]  max_gust_speed_mph [ INTEGER]  precipitation_inches [ INTEGER]  cloud_cover [ INTEGER]  events [ TEXT]  wind_dir_degrees [ INTEGER]  zip_code [ INTEGER] 
SELECT city, COUNT(*) FROM station GROUP BY city