15h and 30min then my 38mm sport Goes to power save mode
Do you have background apps running? If you don't need background apps running turn them off. They are a huge drain on the watch and the iPhone battery. Delete any unused apps from the watch. Turn off notifications that you don't want on the watch. After this you should have a watch Taylored to your needs and a battery that will last throughout the day np.
( background apps is huge. If you don't need it turn it off. Most people think they need this but few do. Unless you're watching for an important stock trade and NEED real time most things can wait until you click the app.)