@ghoofie 

The 1750 speed is the combined theoretical speed, but real-world speeds will be different due to a variety of factors.

Extenders do not work like routers do, routers are full-duplex, extenders are half-duplex (can only send or receive data, not both). 

If there is a high-speed mode you can configure that to see if you get improved speeds. This will make one wireless band dedicated to the router, and one dedicated to the client devices: https://www.tp-link.com/us/support/faq/2479/

Configure the extender as an access point mode should get you better speeds, but will require an Ethernet cable going from the router to the extenders Ethernet port: https://www.tp-link.com/us/support/faq/1401/