chomp(my @unsorted = (<DATA>));
my @sorted = sort { 
   @{[(split('-',$b))]}[0] =~ s/\d+// cmp @{[(split('-',$a))]}[0] =~ s/\d+// ||
   (split('-',$b))[-1] cmp (split('-',$a))[-1]
   } @unsorted;
say for @sorted;

__DATA__
ID12-ABC-5.1
ID9-ABC-5.1
ID3-ABC-6.1
ABC-5.1
ID12-ABC-5.1.5
ID15-ABC-6.1
ABC-6.1
ID5-ABC-5.1
ID5-ABC-5.1.5
ABC-5.1.5