First of all no +Duncan Jaffrey
The 15hours is the average total time per charge cycle. Totally. Separate from active.
Active: the average time phone is active per charge cycle. Includes screen on time plus wake locks. This would include background syncing, playing music, phone calls etc. Notice that the active time for current cycle is exactly the total of held awake and screen time.
The second number is the highest screen on time you've ever had out of any single. Charge cycle.