This would allow negatives:

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my $test = {
   a => '-15-19,30,35,120',
   b => '15-17,30,35,40',
   c => '15-18,30,35,120'
};


for my $key (keys %$test) {
   print "Processing '$key'\n";
   $test->{$key} = [
                     map { /(-?\d+)-(-?\d+)/ ? ($1..$2) : 0+$_ }
                     split(',', $test->{$key})
                   ];
}

print Dumper($test);
[download]

And one more with regex:

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my $test = {
   a => '-15-19,30,35,120',
   b => '15-17,30,35,40',
   c => '15-18,30,35,120'
};


for my $key (keys %$test) {
   print "Processing '$key'\n";
   $test->{$key} =~ s/(-?\d+)-(-?\d+)/join(",", ($1..$2))/eg;
   $test->{$key} = [split(',', $test->{$key} )];
}

print Dumper($test);
[download]