We have 4 identical shelves in which any number of shelves can be empty.
So, we will put 3,2,1,0 shelves empty one by one.
Also, the non-empty shelves won't require internal arrangement as all the shelves are identical.
3 Shelf empty: (8,0,0,0)→1 way
2 shelf empty: (7,1,0,0)(6,2,0,0)(5,3,0,0)(4,4,0,0)]→4 ways
1 shelf empty: (6,1,1,0)(5,2,1,0)(4,3,1,0)(3,3,2,0)(4,2,2,0)]→5ways
0 shelf empty: (1,2,3,2)(2,2,2,2)(3,3,1,1)(4,2,1,1)(5,1,1,1)]→5 ways
Total =15 ways