The theoretical speeds over wifi are very fast - 2.4 GHz wifi is slower than 5 GHz, but even 2.4 GHz can (in theory) offer 300 Mbps. Here in the real world speeds are invariably much lower, but even so, you should be able to get a 60 Mbps wifi connection over 2.4 GHz, and 90 or a lot more on 5 GHz.
So your 6-9-13 Mbps is rather pitiful, and suggests that you have either got a booster problem, or a wifi environment problem. We can help you out, but we'll need a bit more detail on the property size, shape, age, what hub you've got, whether you've done stuff like rename the 2.4 and 5 Ghz channels, what speed you see on a wired connection from a PC or Mac connected to the hub by a network cable, what devices are reporting these wifi speeds, and things like this.