Nested Aggregation Not Allowed

[QlikNewbie15]

hello everyone, 

I'm just new here to Qliksense and was hoping to get some insights on how I could make this expression correct. I am trying to get the quotient of the sum of 2 fields from last month and return the value of 1 whenever the answer is less than or equal 15.

When I use this expression I get the nested aggregation not allowed:

Count(If(Sum({$<[YearDate] = {'$(=Year(Today()))'}, [MonthDate] = {"$(=Month(AddMonths(Today(), -1)))"}>} [Answered Phone in Seconds]) /
Sum({$<[YearDate] = {'$(=Year(Today()))'}, [MonthDate] = {"$(=Month(AddMonths(Today(), -1)))"}>} [Total Phone Calls]) <=15,1))

And when I add the Aggr() function it says that it only takes at least 2 parameters.

Count(Aggr(If(Sum({$<[YearDate] = {'$(=Year(Today()))'}, [MonthDate] = {"$(=Month(AddMonths(Today(), -1)))"}>} [Answered Phone in Seconds]) /
Sum({$<[YearDate] = {'$(=Year(Today()))'}, [MonthDate] = {"$(=Month(AddMonths(Today(), -1)))"}>} [Total Phone Calls]) <=15,1)))

Can someone help me correct my expression?