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.
Thanks!