Really slow transfer from Admin PC to Laptop

I have 2 desktop computers and one laptop on a network, all three are also part of a Homegroup. When I try to copy files from the main Admin PC to the laptop it slows down to less than 15KB/s. I thought perhaps it was the wifi reception but even when connected with Ethernet it's still terribly slow to the point that a 300MB folder takes 2 hours (estimated time). I end up cancelling the...