@Franco1har Hello, 

TL-WPA4220's (AV600) network interface is of 100Mbps (Fast Ethernet port), so the speed come into /out are capped within 100Mbps. 

After traveingl through the long house powerline, signal will get reduced and speed will lose again. To check whether the speed is normal, please download tpPLC Utility here or tpPLC APP and check the powerline rate between 2 units. . Here is a related FAQ explaining the Powerline Rate and Actual speed of the Powerline Adapters: 
https://www.tp-link.com/support/faq/2928/

Since your ISP bandwidth is over 100mbps, you may also consider upgrading to Gigabit powerline KIT, like AV1300 Wi-Fi kit to utilize the router's good speed.