The PRO mode on the Galaxy Note 5 lets you have full control on the camera's settings while shooting. To manually change shutter speed on Galaxy Note 5, do as follows:
1. Open the Camera application on your Note 5
2. Tap the Mode button, which is next to the shutter button
3. Now, select the PRO mode
4. There you should see a bunch of new camera settings, which one of them is the Shutter Speed (The shutter speed icon is next to the ISO icon)
5. Tap the option and you can adjust the shutter speed from 10 seconds to 1/24,000 sec.