The 22KB/sec download speed is coming from the Internet to you. This is not the speed you are getting over your wireless network connection. If you look, you'll see you are only able to 'max' at 10 MB/sec. That is well below 'G' speeds. That is becasue you are able to move things across a small local network much faster than you are able to get them from the interent. Until your download speed from the internet reaches 55 MB/s your router will not hold you back in terms of downloading from the internet. You also have to keep in mind your location versus the location of the download server. That Ubuntu has to be stored some where and your computer has to go out and pull it back to you across the interent. Depending on where the server is, all that traffic has to find it's way back to you. This means it's going to be going out across the interent and running through multiple routers and all kinds of stuff can happen to it.
If we look at the speed of the internet and the quality, I'd say that it seems about right. Just my opinion.
Just remember that the router's 54 MB/s is the 'network' speed or the speed 'inside' your house and the 10 Mb/s is the 'Internet' speed or the speed 'outside' your house.