Can you show a hexdump of your input file? I tried to create it by reverting the process (i.e. I generated it from a UTF-8 input) and the output of your script was exactly the same as the original UTF-8 input.

$ xxd utf.in
00000000: 4372 c3a8 7665 63c5 9375 720a c592 0ac3  Cr..vec..ur.....
00000010: 860a c3a6 0a                             .....
$ perl -we 'binmode *STDOUT, "encoding(iso-8859-15)";
            open my $IN, "<:encoding(utf-8)", "utf.in" or die $!;
            print while <$IN>;
           ' > iso.txt
$ xxd iso.txt
00000000: 4372 e876 6563 bd75 720a bc0a c60a e60a  Cr.vec.ur.......
$ ./1130501.pl
$ diff utf.out utf.in
# No output
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