Thanks @AmeliesUncle
Since my W-4 shows NRA at step 4(c), I don't think the standard deduction is considered as it is not applicable to NRA.
I will check with employer if they can modify withholding calculations to consider standard withholding with NRA status. They use ADP so I am not sure it can be done.
I had previously considered the other workaround of having $15K in step 4(b) but I was confused if it was correct because this $15K is kind of standard deduction and step 4(b) says "deductions apart from standard".
