Mac book Pro is very slow on wifi connection I have three computers in my home. My old computer is a lenovo w530 running windows 10 and my new computers are a 13'' and  15'' inch macbook pro 2015.

All computers are connected to the same wifi router.

if I connect my windows machine and my 13'' macbook pro to www.speedtest.net it report a internet connection speed of Download: 57.65 Mbps Upload: 57.96 Mbps 

when I do the same thing on my 15'' macbook i see connection speed of Download: 3.2 Mbps Upload: 0.59 Mbps

Why is 15'' mac so slow for wifi as compared to my 3 year old windows and 13'' inch macbook pro?

Edit:: Here are the details requested below

RSSI: -37dBm
Noise: -93dBm
TxRate: 117 Mbps
MCS Index: 15
CountryCode: US
Excellent work with the details. The transmit rate and MCS index indicate that your mac has a high-speed connection to your router and that it's not an interference issue.

My next step would probably be timing me file transfer using Wi-Fi from the Mac to the PC or vice versa. You can enable filesharing on the Mac quite easily. download some YouTube movie from the Internet so that you've got something that will take 15 to 30 seconds to transfer so you can time it with the stopwatch. 

It's hard to guess whether flash that runs the speed test.net simply running slow or you've actually got a legitimate speed issue with the Mac. 

You'll also want to watch the activity monitor and the console application to see if you have io errors and if the network throughput matches the disk io which should all matching your benchmarking test.