Let's use a little logic. Any number divisible by both 3 and 5 will be divisible by 15. You don't need to check for both 3 & 5, you simply need to check for 15.

Declare @Counter int

Set @Counter = 1

While @Counter <= 100

  Begin

     Print Case When @Counter % 15 = 0 Then 'BizzBuzz'

           When @Counter % 5 = 0 Then 'Buzz'

           When @Counter % 3 = 0 Then 'Bizz'

           Else Str(@Counter)

     End

     Set @Counter = @Counter + 1

  End