First, that Netgear works well. I have one. It only works over 2.4 GHz (not 5 GHz), but it will transfer data faster than the built in wireless in the PS3.
As Glocks said, when I mentioned the 15 Mbps for your Internet speed, that was my estimate (based on my in home performance) of the speed that you'd need before you'd exceed the PS3's built in capability. At 3 Mbps, you really don't need the Netgear. However, if you decide to stream HD video to the PS3 from something in your home (like a PC), that Netgear will make a very noticeable difference.