I obtained my Galaxy S5 about a month after it came out. Since I have owned it the Wifi hotspot feature has been extremely slow (< a few kb/s).
If I tether the phone, the speed is excellent, and the internet speed on the phone is perfectly fine. This problem only happens when using the Wifi hotspot functionality. Another interesting fact is that if I use the hot-spot at the slow speed for more than 30-45 minutes, the wifi hotspot starts working at full speed after that time. This occurs without changing anything on the phone or my computer. To validate this isn't any issue with my computer, I have tried this with multiple devices and experience the same slowness issues.
My hope was this was firmware or software issues, but I have gone through a couple rounds of updates on the phone and haven't seen anything change. There was another post asking me to power down and remove and reinsert the SIM after 30 sec. I did this, but it didn't have any impact.
Please let me know what suggestions you might have to fix this problem.
While I can't tell you why it's not working for you, I can assure you it should be able to provide decent speed as a WiFi hotspot. I generally get mid-20mbps in XLTE areas via WiFi which is about as good as my cheap laptop gets thru its wireless adapter when connected to any wireless network. I've hit over 80mbps tethered.
If I were you, I'd look at possible interference sources in your area. Are there a lot of WiFi hotspots in range? Old 2.4Ghz wireless phones are also a source of trouble. Could be a neighbor's gabbing on their old phone a lot and you get a speed bump when they hang up.
I appreciate you sharing your experience. In terms of my location affecting it, I travel a lot and the problem exists between states and locals. Some places have no WiFi signals and others have over a 100 crammed together. Regardless, the problem remains.
I brought this up through Verizon and they said they hadn't had anyone with similar issues and that there is likely something wrong with my phone. They are sending me a replacement and I will see if that fixes the problem.
Just had this same issue on mine. Glad I came across this post! Had to tien on developer options and uncheck "stay awake". Hopefully this fixes it. We'll find out tonight...