Sloooow speed of transfering between PC's

I transferring between two win 10 PC’s. My from is on a standard HD through USB 3 while my to is to SSD memory . I’m using drag and drop and have selected all data (127GB) on one partition to a partition on the other PC. My transfer rate calculates to 15GB/hr. Why so slooooow? I could be doing better using network to network on Ethernet.