monotone_gray
Purchasing privilege only means that you are purchasing the privilege to unlock and read X advance chapters ahead of normal readers.
So if you buy the 15 advance chapters tier, it doesn't mean that you will be getting 15 extra chapters daily. You will only get the initial extra 15 chapters on the first day that you purchase the Privilege tier. This is to get you to be 15 chapters ahead of normal readers.
What happens afterwards is that you will be getting the normal daily updates, as usual. If the novel is updated with 2 chapters daily, then you'll also get 2 chapters of that novel daily, with the only difference is that you will still be 15 chapters ahead of the normal readers.
So for example, if normal readers are on chapter 10, as a privileged user that bought the 15 advance chapters tier, you would be on chapter 25. When normal readers get 2 chapters in the daily update, which means they get chapter 11 and 12, as a privileged reader you will be getting chapter 26 and 27, and so on, until your privilege access expires at the end of the month.
After your privilege access expires, it simply means that you will go back to the chapter where the normal readers are on. So in the case of the example above, you'll go back to chapter 12. If you don't repurchase the same privilege tier in the new month, it means that you will have to wait several days before the daily updates for the normal readers would catch up to where you were when you were still a privileged reader (in the case of the example above, chapter 27).
If you don't want to wait and want to just resume to read from where you left off before your previous privilege expired, then you will need to repurchase the same privilege tier again in the new month (in the case of the example above, the 15 advance chapters tier).
Hope this clears it up a bit for you.