Increment every 15 rows in excel sheet using VBA

I know it has been two weeks since you posted, but fwiw, I think this could help.

Using a step value of 15 in a for loop and incrementing the starting value in each iteration should take care of what you need easily. This first code is hard coded with the values you provided and should be easiest to follow.

Sub IncrementEveryFifteenRows()

'Declare startValue to capture the value of E15
Dim startValue
startValue = Cells(15, 5).Value

'Loop to jump to every fifteenth row, incrementing startValue each iteration
For i = 15 To 200 Step 15
    Cells(i, 5).Value = startValue
    startValue = startValue + 1
Next i

End Sub

This next code adds a level of abstraction by incrementing every fifteenth row of the selected range. This way, you could begin and end at whichever row you like. For instance, if you select B3:B100 and the value of B3 is 5, then you will set B18 as 6, B33 as 7, B48 as 8, B63 as 9, B78 as 10, and B93 as 11.

Sub IncrementEveryFifteenRows()

Dim startValue
Dim selectedRows

'Using Selection, cell references are relative to the selected range 
'and not the worksheet as a whole
startValue = Selection.Cells(1, 1).Value
selectedRows = Selection.Rows.Count

'Loop to jump to every fifteenth row, incrementing startValue each iteration
With Selection
    For i = 1 To selectedRows Step 15
        .Cells(i, 1).Value = startValue
        startValue = startValue + 1
    Next i
End With

End Sub

This code can be abstracted further with user prompts to gather values such as step value, increment value, specific rows on which to begin and end, and which column this should apply to. That would just require declaring more variables to put in place of the hard coded numbers in the first example.

Hope this helps, and good luck.