Im on a wireless conenction, and in the same spot as always in the house. my normal download speed is 20 Mbps and now it is 15 Mbps, I checked for viruses and there are none. I did change my router channel from automatic to 1 (to discourage the evil microwave from blocking my internet). does channel one have a bad reputation for slow speeds?
When you say wireless connection do you mean you have wireless internet, or you're connected to a fixed line service (Cable/ADSL) via a wireless router/modem?
If it's wireless internet then there could be some local interference that's dropping your signal quality. If so you could wander around the house and monitor your connection speed to attempt to locate the source.
If it's ADSL then try resetting your modem. It's possible that it synched at a slower speed due to noise on the phone line. I find when my ADSL at home drops out due to too much noise on the line it will try to connect at a slower speed so that there's a higher noise margin, meaning that it will take more interference to interrupt the connection.
A speed test will only tell you what your computer can obtain at that current time. If you look on your modems setup page you should be able to check the router status, which will show downstream and upstream connection speeds, usually in kbps. That will give you a more accurate estimation of what you SHOULD be able to download at, if you're the only one on the network.