I should notify you about one catch regarding the schedules from STR (the airport) and ZWS (the central station): There are two lines of S-Bahn trains running on the route with a total of 4 trains per hour, but unfortunately they don't leave in 15-minute intervals but there will be two trains within 10 minutes and then 20 minutes without any train.
By the way, if you don't already have your train ticket for the onward journey, you need to buy a ticket valid for three zones to get to ZWS. If you are travelling with a companion and both of you will also be returning by S-Bahn from ZWS, it is cheaper to buy a ticket valid for 4 rides (stamp twice to make it valid for two people).
Ah, and something more: In concourse 1, there's a ticket machine in baggage claim (next to the exit), so you may even buy your S-Bahn ticket while still waiting for your luggage.