If you have a Galaxy S5 on Verizon and you recently updated to Lollipop, you might want to clear you cache partition. You can do this by removing your battery and putting it back in. Hold the volume up, home, and press the power button. Keep holding the buttons until small text appears on the screen. Then use the volume buttons to select wipe cache partition and use the power button to select it. Once done reboot phone from this menu. It should preform much better.
If that does not work or your phone is still slow after a few days, it might be best to do a factory data restore.
Let us know what your experience have been.