@Shubham do you have a cordless landline telephone in your house too? Try switching it off and see if it makes any difference?
@Shubham AirDroid: Remote access & File – Apps on Google Play
install this on your mobile and transfer a file from pc to mobile.
Open App on mobile
On pc in browser open http://192.168.0.XXX:8888/ (192 is the ip allocated to your mobile by router)
(Both mobile and pc should be on same network)
Check transfer speed on pc using task manager.
I just cannot understand the reason behind it.