Can get 15 by getting

3,3,3,3,3,0 giving 6 possible arrangements

3,3,3,3,2,1 giving 5 + 5 + 5 + 5 + 5 + 5 = 30 possible arrangemnts

3,3,3,2,2,2 giving 4 + 3 + 2 + 1 + 3 + 2 + 1 + 2 + 1 + 1 = 20 possible arrangements

Giving 56 possibles for score of 15

Can get 16 by getting

3,3,3,3,3,1 giving 6 possible arrangements

3,3,3,3,2,2 giving 5 + 4 + 3 + 2 + 1 = 15 possible arrangements

Giving 21 possibles for score of 16

Gives 77 possibles for score of 15 and 16

The trick is to think systematically (though I believe there are formulas out there that will provide short cuts for working out each possible arrangements).

Fix one number and work out the posssible arrangements. Then move it to another position and fix it and work out possibles, etc, etc