Assuming you always want 15 items per page, I would just do something like:

my $page = url_param('page');
my $per_page = 15;
if($page) { 
    my $min = $page == 1 ? $page : $page_per * ($page - 1);
    my $max = $page_per * $page;
}
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This gives you some overlap (1-15, 15-30, 30-45, etc.) If you don't want overlap, it's easy to modify.