With WiFi you will never get real world speeds (or throughput) near to the advertised speeds of the device. When you read on the box "up to 150Mbps" this is not talking about throughput, but rather connection speed.
The connection speed is how fast the data can be transmitted and received between two devices, however there are a number of factors that separate this speed from what normal users would consider their throughput. Ultimately, if you get throughput that is 30-40% of the best connection speed, you are doing really well, but I would expect in most cases that this would be lower.
Leave it at that if you want, but if you are interested, here are a few of the reasons throughput will never match connection speed (there are others, but this can be a very involved conversation).
First, WiFi utilizes a shared medium. Since they work by sending a radio signal into the air, only one device on the same frequency in the same area can talk at any given point in time or they will interfere with each other.
While not a perfect example, think of this as driving in your car on a long trip and listening to FM radio. If you get to a point where you pick up signal from two radio stations using the same frequency, they start to interfere with each other. This may create static, the sound cutting out, etc.
Since most network traffic is a two way communication, even with only two devices in an area (router/accesspoint and one station), this will have a impact on throughput. 802.11 devices are programmed to share the RF, so more devices means the impact is greater. This can include other nearby WiFi networks as well.
Second, you will typically not get the highest connection speed at all times. As you move further from the router/access point and the signal strength decreases, the connection speed will reduce. Even if you disable the older 802.11 technologies, the lowest connection speed for 802.11n is 6.5Mbps.
Third, there is "management" overhead for wireless. An example is the probe and beacon frames which make it possible for your device to "see" what wireless networks are available. The list also includes 802.11 associations, authentications, acknowledgements, protection mechanisms, and so on.
While typically these won't make up a lot of traffic, one study sponsored by Ofcom (Great Britain's equivalent to the US's FCC), showed that in some urban areas the majority of traffic in the air was made up of management traffic. A bit technical, but if you are interested, you can find it here: http://stakeholders.ofcom.org.uk/binaries/research/technology-research/wfiutilisation.pdf
Don't read too much into this study, as there are a number of factors one needs to consider outside of the data they capture. For instance, capturing traffic from one access point in a faraday cage with no client devices would result in 100% of the traffic being management.
I can go on, but hopefully that illustrates some of the factors to consider.