In cases like this, where the primary purpose is something straightforward (as stated in the question), I'd prefer to split up the code into 'obvious' subroutines, so that the main block of code looks something like this...

my $dbh = DBI->connect($connection_string);
my $dbh2 = DBI->connect($connection_string2);
while (1) {
  my $count = get_table_count($dbh);
  do_table_copy($dbh,$dbh2) if $count;
  sleep(15 * 60);
}
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Note that you don't need to sleep *only* if $count == 0 - if you perform the copy, presumably you're not going to want to bother checking again for another 15 minutes.

Cheers, Ben.