while (<DATA>) {
    chomp;
    print join(" + ", expand($_)), $/;
}

sub expand {
    my $input = shift;
    $input =~ s/[^-\d,]+//g;
    $input =~ s/-/../g;
    my ( %tmp, @tmp );
    @tmp = ( eval "$input" );
    @tmp{@tmp} = (1) x @tmp; # dedupe
    return sort { $a <=> $b } keys %tmp;
}

__DATA__
1,7-10,3-5,15
or even ... my $input = "1,7-10,3-5,15";