If you use in your household a wireless repeater to supply the entire house with a strong Wi-Fi network, then you may have the following problem with your Samsung Galaxy S5:
The Samsung Galaxy S5 remains connected to an access point until the connection is too weak, although a stronger access point is nearby. Despite the stronger wireless signal nearby your phone stays connected with the old Access Point. Thus, of course, your Internet speed within the WiFi on the Samsung Galaxy S5 is not as fast as it could be.
If this bothers you, then you should try the following useful app:
The app is called "Best WIFI" and regulates precisely this problem. The app checks if a stronger wireless signal is available, and thus connects automatically, if you have previously set. The app "Best WIFI" can be downloaded for free from the Google Play store and is definitely worth a test if you have to deal with the above mentioned problem.
You should now have the best possible connection strength with WiFi repeaters and your Samsung Galaxy S5 everywhere .