@Srjsonu26 

Thank you for your for proving the speed test result. As Range extender receives data from the router and then forward it to the connected clients and speed will decrease during the transmission,  the speed of router at RE's location is quite important. When test router speed, make sure you test Router speed at RE's location. 

1. Please use a Wifi SSID for RE that is different from the router, and test RE's 5Ghz wifi speed

To check if RE has reasonable speed, can  you help provide the information below : 

1. Speed test result from routers at the RE's location, this is to check how much speed range extender could receive speed from the router 

2.  Wi-Fi  link speed when the device connects to router  (How to check the associated/link speed on a wireless client)

3. Speedtest result of RE's 5Ghz Wi-Fi  

4. Wi-Fi  link speed when a device connected to RE

Thank you.