My realtime credit usage never goes up to 1 cent, but then suddenly I’ve lost 15 cents? Is there an issue?
I’d like to add that previously I played for 3 days without losing 1 cent, and now suddenly I’ve lost 15 cents all at once.
Which mudfish node did you use? Normally our traffic charges happens when usage data is collected to the log master server. But it happens in as the lazy manner to avoid heavy log at the server so the collection could take up to 1 ~ 3 hours. However in your case, you said it takes 3 days so it’s weird for me. 
I use automatic (or simple mode I think it’s called?) It’s strange, because looking at my graphs of data used it’s wideley different from day to day, even with similar playtime.
You can check your traffic history as you enabled the Connection Log.
Status - Traffic
Accounts - Traffic Usage
Status - Access Log
Accounts - Access Log