Unable to count values in column

I am tring to count the amount of items that took <15 etc

The code I'm using is:

# Cases <15 days = CALCULATE(
                            COUNT(Deferrals[regardingobjectid]),
                            FILTER(Deferrals,
                            Deferrals[TimeinDeferral] = "<15"))

I'm getting this error message

Can anyone offer a suggestion to get around this? 

Is there a way of doing this without using Variables?

Thanks