24Mb/s on ethernet and below 2.0Mb/s on wireless

I have already tried looking for solutions in forums and tried a lot of them but nothing seems to work for me.

I have a D-Link DCM-202 modem and a Cisco Linksys E1500 router. I do speedtests and I'm getting 24Mb/s on ethernet cable, which is what I should be getting under my internet plan. But once I go wireless the speed just drops significantly to below 2Mb/s, Even when I'm right next to the router. I began to think that maybe it was my wi-fi adapter but I looked up the model for Intel Centrino Advanced-N 6230 and it seems like I have a new and fairly good adapter, since I just bought this laptop for a few months.

I do have the router and the modem connected next to all my home electronics like TV, stereo, PS3, dvd and stuff like that, but I've never really had this problem before, not with my old laptop. But ever since I got this new pc, I've been having trouble getting wi-fi speed at home, AND having trouble connecting at my school's campus while other people connects just fine.

But I'm not an expert on any of these hardwares so I'm wondering if anyone can confirm the cause of my issue here?