Medication 15 days per column in Excel

I'm asking on how can i add 15 days interval depending on start date in this case its 01/21/2023 and it will skip on the other column for another 15 and so on.

This image is on a seperate sheet in excel im just gonna use vlookup to get the value per cell in a another sheet to display it or use pivot table.

You don't need VBA for this, it can be done with formulas.

Imagine the following worksheet, where B1 is the start date and B2 the interval (note your interval in your example is 14 not 15):

You can then use the following formula in B5:M35

=IF(INT((DATE(YEAR($B$1),B$4,$A5)-$B$1)/$B$2+1)=(DATE(YEAR($B$1),B$4,$A5)-$B$1)/$B$2+1,(DATE(YEAR($B$1),B$4,$A5)-$B$1)/$B$2+1,"")

to get the desired result.

Note that the months need to be numbers too.