The machines are usually shipped with a 50mm lens, sometimes a 40mm, from what I have read (those numbers are approximate, I think it's all really in inches converted).
So, while it would make sense for you to have a 100mm lens with your 150w to allow more straight cutting in thicker materials, probably was not what it came with.
Take a look at the diagram attached to see what is best for you with what you cut. I'm sure there is a trade off between best for some things and the best all around.....I'll find that out myself once my machine arrives.
Also, I gather there are techniques to test the focus other ways (ramp test I saw one poster refer it it as), so you can look up those and try to check to see what you have.
I don't remember where this picture attached came from, looked for a link first but could find it again.