If you want dedicated throughput, you have to do wired. There are too many variables to wireless. You could be running into 2.4 gHz interference, the other people could be eating up a lot more bandwidth, there could be some other anomaly.
If this is 802.11g, the advertised rate is 54 mbps. The real throughput put of .11g is roughly 15-16 mbps, and you have to realize this is divided every time someone else is on. This is also half-duplex. Wireless AP's can only talk or listen, then can't do both at the same time.