Well, 150 Mbs is not slow, in fact it's almost certainly considerably faster then you Internet connection. You need to do some diagnostics.
First establish that you have a decent speed on your Internet connection by connecting by cable and running a speed test.
http://www.speedtest.net/
If your wired connection speed is OK, you need to look at the quality of signal you are getting. Is the speed OK when your computer is near the router? Do you have any other WiFi devices (such as a table or phone). Do they get a decent speed when positioned near your computer?
How far is the computer from the router - are there any potential obstacles to the signal (such as concrete or stone walls, etc)
Finally, you may be experiencing interference from another nearby WiFi (such as your neighbour's), in which case you could try changing the channel on your router.