Originally Posted by PorkRind

The card is capable of either 10 megabits or 100 megabits per second, depending on the capabilities of the switch/router/cable modem/etc. it's plugged into. I suspect your internet service provider provides a downlink speed of 15 megabits per second, and you should theoretically be capable of reaching that transfer rate assuming the segment of the internet you're transiting isn't otherwise congested.

It's been a very long time since cable modems supported no more than 10 megabits per second, and in any event your speed tests should still be exceeding 2.5 megabits per second . . . even if you have a vintage modem.

It's possible that you're having an auto-negotiation problem between your ethernet card and cable modem. You may be able to modify the adapter settings to lock the speed of the card to 100 megabits/second, full-duplex. Try that and see if you get better results. If not, set the card for 10 megabits/second, also full-duplex and see what happens.

You might also consider springing for a GigE card (1 gigabit speed). If your cable modem is a current model, it likely supports connections at that speed, but it won't allow you to exceed the speed you've contracted for through your ISP. GigE cards are less than $30 for PCI and PCI-e motherboards. I recently purchased a Netgear GA-311 from Newegg for $23.