After the update, the camera is very quite while powered up. When you press the shutter button to take a picture, the image stabilization system kicks in, and you'll hear the familiar hum as long as the shutter button is pressed halfway or full. It's a good solution.
Logic would say that this change would also have a slight improvement on battery life, even though that isn't stated in the documentation. Another benefit of firmware V 1.5 is improved 5-axis stabilization when using OM lenses with an adapter, even in movie mode. This enhances a big advantage of the OM-D, which is image stabilization for any lens you put on the camera.
The firmware is easy to apply. Just use the camera updater app. In my initial testing, everything is working great.
Take a look at the Olympus Micro Four Thirds Gear Guide for an overview of cameras, lenses, and accessories.