On more than one occasion I've seen you post and give horrible information, in most cases, very wrong because you don't know any better. If you don't know something, DON'T COMMENT ON IT.
0.15V is a big difference when it comes to batteries as small as ours. In a car battery, sure, 0.15V isn't that big of a deal, it's less than 0.01% of a difference, something that can naturally occur with impurities in the lead/acid components, magnetic shift or hitting a speed bump too fast. However, on a battery the size that's in our phones? That's a 3% difference. 3% variance is MASSIVE in relative sizes.
I'm not saying don't help anyone, but don't fake answers in hopes someone clicks your thanks button.
In the past, have you flashed a 3rd party kernel at any time, for fun or testing, or for daily driver use? (Even if you're stock now)
How are you plugging the device in - USB port on a computer? USB port on the side of a surge protector? If it's a computer port, is it USB 2 or 3?
Are you using the stock charging block and stock cable that came with the phone? A 3rd party solution like Belkin, etc.?
If you have access to one, plug into a car cigarette lighter, either Sony or 3rd party, do you see a change in the overcharge values? What about a magnetic charging cable?
Have you opened up the phone and tinkered with anything?