Are you a hacker? Are you not worried if your code looks like crazy old magic? Then you'll love this solution:

sub test0 {
    return ((($_[0] & $_[1]) * 2113665) & 17895697) % 15;
}
[download]

(Go ahead! Check that it's correct for all input values!) Benchmarks on my computer, against your code and [id://hv]'s:

          Rate Test4 Test5 Test7 Test6 Test0
Test4  64233/s    --  -33%  -33%  -52%  -72%
Test5  95523/s   49%    --   -1%  -29%  -58%
Test7  96399/s   50%    1%    --  -28%  -58%
Test6 133602/s  108%   40%   39%    --  -41%
Test0 227756/s  255%  138%  136%   70%    --
[download]