I suspect you have made a 2.4ghz connection to the disc ? (mind you, it still should be faster are you measuring mbits per second or mbytes per second?)
You cant split them (unfortunately) so first check what type of connection you have.
Right click on the wifi icon, then go to open network and internet settings, thenwifi and then hardware properties and check.
What disks are you using ?, mini, white or black ?