This app was mentioned in 11 comments, with an average of 1.82 upvotes
I don't know. The hint here is that No, it won't charge faster than 15 Watts, because that's the charger they include and it already limits when to go to that maximum.
But I haven't tried it. You could run something like 3C Battery Monitor to watch the charge rate and infer it from the mA going into the battery.
I have the same battery, and I downloaded a widget called Battery Monitor. After a full charge and a reboot, it now detects my battery properly, and has very few quirks, none of which are a very big deal. I bought the full version after a few days of using the free one, since it's a fantastic app, and fully solved my problems.
https://play.google.com/store/apps/details?id=ccc71.bmw.pro&hl=en
Maybe 3C Battery Monitor Widget? I've never used the app; but looking at the screenshots it does appear to display capacity >> 2116 / 2300mAh.
Not free, but the one have always used with extended batteries is Battery Monitor Widget Pro by 3c. They have a free version too, and while does have the custom mAh support, which can help with accuracy, it doesn't have the voltage based calculation support that the pro version has, which can lead to the best accuracy with very large batteries. And a few other features aren't in the free version. But it's still quite capable.
Your battery is probably discharging faster than it can charge, probably because the USB cable and power brick isn't charging at the maximum possible amperage. I've had good luck with Anker brand USB power bricks and these USB cables. Even though rapid charging devices max out at 2A, mine rarely charges at anything higher than 1.5A.
I don't know what device you have, but since I'm an Android guy, I would recommend Battery Monitor Widget Pro. It will tell you how fast your battery is (dis)charging.
https://play.google.com/store/apps/details?id=ccc71.bmw.pro
There's also a free version.
https://play.google.com/store/apps/details?id=ccc71.bmw.pro MN This one you can use the free version
https://play.google.com/store/apps/details?id=ccc71.bmw.pro
With this app you can create a widget with lots of different battery info. I know it's not in the status bar but it will show a variety of things. I have percent charged, Batt temp, percent used per hour, how long it's been plugged in (once unplugged it shows time on battery) and time remaining till full charge. I have pro.