Question:
Which position did Patricia de Lille hold in Sep, 2015?

Context:
 Patricia de Lille holds the position of Member of Provincial Parliament of Western Cape from Sep, 2010 to May, 2011. 
 Patricia de Lille holds the position of mayor of Cape Town from Jun, 2011 to Oct, 2018. 
 Patricia de Lille holds the position of member of the National Assembly of South Africa from May, 2019 to Dec, 2022.

Answer:
mayor of Cape Town