just posting my experience, like the captain...
I have used 2 different desk top machines, an older machine with windows xp, and a newer 64 bit windows 7 machine with no issues at all...
am typing now on a 4 year old Acer laptop tethered to a Samsung galaxy S4 phone via hot spot app and am having no problems at all, even though I only have two bars for signal strength as I live 5 miles from the nearest small town with cell tower, I am getting the 4g backbone on this phone and do all the time. However, my wife and son have I phone 5s' and theirs can vary from 4g to 3g for whatever reaons.
perhaps those variables can affect some of your down load speeds
as a side note, I do not use my cell phone itself to get on the www unless if absolutely necessary for a few quick searches, that because as I age I hate using reading glasses.
in the past, before Verizon expanded its 4g backbone from the 3 g, I would have slow downs on the old backbone, I attribute that to signal strength and any other conditions that would affect the radio wave from tower to phone.
best of luck keep trying, hope you figure it out