The Bosch unit is actually an EVSE, or EV supply equipment. Essentially a fancy wall-mounted AC supply that plugs into the car. The car has a charger onboard that converts AC power to DC to charge the battery. Slightly pedantic, but it's important to understand for exactly the reason you describe: an EVSE that can supply more current won't help you charge faster because the 16 amp EVSE can supply all the current that the S onboard charger can use (3 kW = 240V 14A iirc).

The cost difference is relatively small for a higher-current EVSE. i.e., it costs $120 additional to upgrade to a 30A 18' Bosch unit. The 16A unit is plenty fast for overnight charging, so as long as you're comfortable with your charging requirements then it should work just fine.