Hello  @puneet.mishra 

For a single-band range extender, real Wi-Fi speed around 60-90 Mbps are as expected. 

 Range Extender works in 'half-duplex' mode in extender mode,  it can only talk to the main router or the wireless client device in either way, not the same time, the link speed at physical layer will cut to half. Real 2.4Ghz speed could be around 50% of wireless link speed. 

If the router is a dual-band Wi-Fi router, you could consider a dual-band Wi-Fi router for higher speed.  

If you could wire extender to router via Ethernet cable and use RE in Access Point mode, the speed could  be higher.

To check if the speed is reasonable, you could refer to the thread below to troubleshooting and help provide information below: 

 What should I do if Internet speed becomes slow via Range Extender?

• Check the Wi-Fi link speed between range extender and client
• Speed test result from router 2.4 Wi-Fi at RE's location;Speed test of RE 
• Router's 2.4Ghz Wi-Fi speed test result at extender's location (RE's received speed)

How to check the associated/link speed on a wireless client