If a WiFi connection on a laptop or something is not getting speeds higher than 12-14Mbps check the configuration of the Wireless Network Adapter and be sure that 802.11n is enabled.
Sometimes this is in the advanced settings of the Wireless Network Adapter and may be called ad hoc 802.11n mode. Be sure it is enabled.
Otherwise if the Wireless Network Adapter is running in 802.11g mode speeds should not be expected to be much higher than 12-14Mbps on a speed test.