Public Sub Main()
    Dim a As String, b As String, t As Single

'    a - входная строка
    a = String( 10000000 , "a") & "home"
'    b = строка для сверки
    b = String( 10000000 , "b") & "abcdefghmopuyt"
    
    t = Timer
    Debug.Print MyFunc(a, b), Format$(Timer - t, "0.0000")
End Sub

Public Function MyFunc(a As String, b As String) As Boolean
    Dim ma( 255 ) As Boolean, mb( 255 ) As Boolean
    Dim i As Long

    For i =  1  To Len(a)
        ma(Asc(Mid$(a, i,  1 ))) = True
    Next i
    For i =  1  To Len(b)
        mb(Asc(Mid$(b, i,  1 ))) = True
    Next i
    For i =  0  To  255 
        If ma(i) Then
            If Not mb(i) Then Exit Function
        End If
    Next i
    MyFunc = True
End Function

    '    a - входная строка
        a = "home"
    '    b = строка для сверки
        b = "abcdefghmopuyt"