Payroll is not suited to "read" days as it is more geared to reading Payroll Periods, which in many cases overlap different months.
You could create a Custom Information WT (let's call it 9CLD - Calender Days Left) and a Constant in table view V_T511K (let's call it ZDAYS, with a value of 365).
Through a Payroll Calculation Rule, starting in the first month you want to consider, you identify the number of days in that month and deduct them from the value of constant ZDAYS to create WT 9CLD, which WT can then be used to process your IT0015 WT. Note that each month thereafter, you must add the number of days in the current month to the value of 9CLD in the last month.
Note this should be done through Time Evaluation if the Payroll Period is not "Monthly".