Speed drops on wi-fi, ASUS router, HP laptop, Mercury USB

Hi all,

First, thanks in advance for the help from anyone and everyone.

My family bought a new router, ASUS RT AC56U, which on Ethernet is pretty decent; It gets 200Mbps + on speedtest.net. However, when I try to go on wifi, no matter what network adapter I use, the speed never breaks 15Mbps which is not exactly sufficient, and drops even more as I move into my room, which is further away and places a concrete wall between my laptop, phone, tablets, and the router. We have one "homeplug" that routes the network via ethernet through our power sockets but this is reserved for the desktop; the speed here is insignificant as the desktop isn't used much...

My current laptop is the HP envy 14 sleekbook (14-k016tx) which supposedly has b/g/n adapter. Also, a few other laptops wanted to benefit from the new router and our 300Mbps internet optic fiber service plan, so we purchased a Mercury MW300TV usb receiver, which detects as a Realtek device [RTL8191SU] for some reason (thanks, China). The CD that came along with it does not include a working driver so I just tried out 3 of the top results I could find on the internet.

I have messed with a lot of settings in vain; my internet connection is still ridiculously slow on wi-fi. Any advice would be appreciated.

I am ready to post any additional information should it be required.

Thanks again in anticipation. Your responses will be read with gratitude.