What is the average speed that people read in English?
According to this website, it's 238 words per minute for non-fiction and 260 words per minute for fiction.
The average length of a novel is 90,000 words, according to this website, which means the average person would take 5-6 hours to finish it.
If you are learning English, even if you are at B2-C1 level, you probably read a little slower. Let's say that you read 180 words per minute. It would take you over 8 hours to finish a 90,000-word novel.
Hence, you can see the benefits of increasing your reading speed!
If you're interested in doing that, you can test your reading speed here. Be warned, you not only have to read a text, but also answer some questions on it!