Unless it's causing problems in your daily life I honestly I wouldn't worry about it. Worrying about reading speed doesn't make sense beyond elementary education or unless you have some objective issue that is clearly causing problems. E.g. someone with dyslexia will benefit from a diagnosis, so I'm not saying ignore problems, but don't look for a problem that likely isn't there based on some figure on a website.
Everyone has slightly different strengths and weaknesses when it comes to cognitive skills and where some people may read faster than you, you probably have some other advantage. I read faster than my husband, he's still better than me at understanding technical info quickly.
Also the term "average" means lots of perfectly normal people will be faster or slower. Without knowing how that figure was arrived at, it's hard to assess if it's even credible or relevant. Can read at a certain pace is one thing, but what about accuracy of comprehension? And was this a short 5 minute test vs. say, a two hour study session where fatigue may slow you down (or indeed note taking, as you mention). I would certainly not expect five minutes worth of study to scale up as far as pace goes.