Even though the tests always have been on wifi, you cannot guarantee anything with over wifi. Things in the environment can change such as congestion on certain wifi channels or interference etc. This change may not be down to you, it could be a neighbour switching channels onto the same one you are using, for example. But these things would impact your wifi performance.
You should first try some wired speedtests and establish what you are actually getting at your router output. If that is 150 mbps, then that determines that your connection is completely fine. Your next step then would be to try and figure out ways to improve your wifi. That could be as simple as trying a different wifi channel. But first, a wired test and then go from there.
