A:Answer By default (in OS 10.11.5 El Capitan), the F14 & F15 keys are redundant in that they change screen brightness - the same as F1 & F2. You can change that in System Prefs, under Keyboard>Shortcuts. You can uncheck them and reassign F14 & F15 to something else (find an item you want to change, click on the F-key text and type the actual F-key or combine with modifier keys.
The key to the right of F15, as stated in previous Q&A's, is an indicator of sufficient / insufficient light for charging. If it lights green, you have sufficient light for charging. If it lights red, there is not enough light for charging. The "Solar App" on Apple's App Store is tied to the button. When launched (by clicking the button), it indicates level of charge currently in the battery as well as a light meter measuring Lux for current charging.