The next payday

Ah yes, the key word is 'Next' Payday.

The first 2 formulas suggested find just the 15th of the current month.
But if today's date is already past the 15th, then we need the 15th of the next month.

So kvsrin's formula is the only one that accounts for that.
But not quite.
It's testing if the DAY(A1) is < 15
This would fail If the 15th of current month happens to be a weekend or Holiday, because the payday would then be the previous working day from 15th.

Here's an ammendment to mine that would work for that as well.
=WORKDAY(EOMONTH($A$1,IF(WORKDAY(EOMONTH($A$1,-1)+16,-1,$A$2:$A$10)<$A$1,0,-1))+16,-1,$A$2:$A$10)

Let's test 3 formulas with:
A1=12-May
A2=13-May
kvsrin's and Jonmo say: 12-May
but mine say: 15-Jun