Isempty with If function in VBA

For 1st part
If you want to test for not empty

If Not IsEmpty(Range("B15").Value) Then

Sub Macro4()

'Giving results what i want
If IsEmpty(Range("B15").Value) Then
    If IsEmpty(Range("C15").Value) Or IsEmpty(Range("D15").Value) _
    Or IsEmpty(Range("E15").Value) Or IsEmpty(Range("F15").Value) _
    Or IsEmpty(Range("G15").Value) Or IsEmpty(Range("H15").Value) _
    Or IsEmpty(Range("I15").Value) Then

        MsgBox ("Error")
    
    Else
        MsgBox ("No error")
    
    End If
End If
'Not giving results what i want

'If IsEmpty(Range("C15").Value) = False Or IsEmpty(Range("D15").Value) = False Or IsEmpty(Range("E15").Value) = False Or IsEmpty(Range("F15").Value) = False Or IsEmpty(Range("G15").Value) = False Or IsEmpty(Range("H15").Value) = False Or IsEmpty(Range("I15").Value) = False And IsEmpty(Range("B15").Value) = True Then
'
'MsgBox ("Error")
'
'Else
'MsgBox ("No error")
'
'End If

End Sub

Another way of writing:
Option Explicit

Sub Macro4()

    'Giving results what i want
    If Not IsEmpty(Range("B15").Value) Then
        If IsEmpty(Range("C15").Value) Or IsEmpty(Range("D15").Value) _
        Or IsEmpty(Range("E15").Value) Or IsEmpty(Range("F15").Value) _
        Or IsEmpty(Range("G15").Value) Or IsEmpty(Range("H15").Value) _
        Or IsEmpty(Range("I15").Value) Then
    
            MsgBox ("Error")
        
        End If
    
    ElseIf IsEmpty(Range("B15").Value) Then
        If Not IsEmpty(Range("C15").Value) Or Not IsEmpty(Range("D15").Value) _
        Or Not IsEmpty(Range("E15").Value) Or Not IsEmpty(Range("F15").Value) _
        Or Not IsEmpty(Range("G15").Value) Or Not IsEmpty(Range("H15").Value) _
        Or Not IsEmpty(Range("I15").Value) Then
        MsgBox ("Error")
    
    Else
        MsgBox ("No error")
    
        End If
    End If
End Sub

In the 2nd part of the code, you didn't have B15. Try this...

Sub Macro4()

'Giving results what i want
If IsEmpty(Range("B15").Value) = False And IsEmpty(Range("C15").Value) = True Or IsEmpty(Range("D15").Value) = True Or IsEmpty(Range("E15").Value) = True Or IsEmpty(Range("F15").Value) = True Or IsEmpty(Range("G15").Value) = True Or IsEmpty(Range("H15").Value) = True Or IsEmpty(Range("I15").Value) = True Then

MsgBox ("Error")

Else
MsgBox ("No error")

End If

'Not giving results what i want

If IsEmpty(Range("B15").Value) = True And IsEmpty(Range("C15").Value) = False Or IsEmpty(Range("D15").Value) = False Or IsEmpty(Range("E15").Value) = False Or IsEmpty(Range("F15").Value) = False Or IsEmpty(Range("G15").Value) = False Or IsEmpty(Range("H15").Value) = False Or IsEmpty(Range("I15").Value) = False And IsEmpty(Range("B15").Value) = True Then

MsgBox ("Error")

Else
MsgBox ("No error")

End If

End Sub