Check if a date doesn't start with a number of day values in Openrefine GREL (General Refine Expression Language)

date_day_not_equal.txt

#parse the date as a string and extract the day, 
#compare it to the string value '1' and '15' and if it's equal to either, respond TRUE else respond FALSE

or((value.toDate('dd MMM yyyy').toString('d'))==toString(1),(value.toDate('dd MMM yyyy').toString('d'))==toString(15))

#to be used as a Facet in OpenRefine