storing data on sql database vs array (mobile apps)

I have a classifieds app for android. It has a list of 4k cities with corresponding zip codes stored in a assoc array like so:

Map<String, String> cities = new HashMap<String, String>();
cities.put("Rio", "32433");
cities.put("Buenos Aires", "54335");

I am in the process of developing the app for the iphone now, using swift and I was wondering, whether I should stick with storing the city data in a array or store it in a database.

Will it make a difference in performance? The app will have fill the array each time the app is launched, so maybe a database integration would make the app launch faster and consume less resources.

If anyone has any advice I would highly appreciate it. Again the list array has about 4k elements/rows.

Thank you!