Maybe you're thinking about 1500 hours instead of 15000. 15000 hours is approx. 5 years at 8 hours a day and you would reach "mastery" level in a lot of subjects (if studying deliberately).
Also, when you are reading you are most likely speaking with your inner voice. If you don't know the proper pronunciation, you may reinforce bad intonation/pronunciation habits. It happens to me when I'm reading a text with names that I'm too lazy to properly read. I just register the shape of the word with the first/last letters and length, then I pattern match in the rest of the text to know who we are talking about and that's it. More then once when talking with friends about books/articles/..., I could not tell the name of the person of interest. If it was written I would recognize it but I couldn't vocalize it.
Also, when you are reading you are most likely speaking with your inner voice. If you don't know the proper pronunciation, you may reinforce bad intonation/pronunciation habits. It happens to me when I'm reading a text with names that I'm too lazy to properly read. I just register the shape of the word with the first/last letters and length, then I pattern match in the rest of the text to know who we are talking about and that's it. More then once when talking with friends about books/articles/..., I could not tell the name of the person of interest. If it was written I would recognize it but I couldn't vocalize it.