Some more information from my testing:
The bottleneck is in the file administrator->components->com_hikashop->classes->product.php
and the part of the code causing the slow load is:
if(isset($element->$field) && is_array($element->$field) && count($element->$field)){
$array=array();
foreach($element->$field as $k => $v){
$array[$k] = (PHP_VERSION < 5) ? $v : clone($v);
}
$variant->$field=$array;
}else{
if($field=='product_name'){
$config =& hikashop_config();
if(!empty($variant->characteristics)){
$separator = $config->get('characteristics_values_separator',' ');
foreach($variant->characteristics as $val){
$variant->characteristics_text.=$separator.$val->characteristic_value;
}
}
}else{
$variant->$field = @$element->$field;
}
}
I believe it is the line $variant->$field = @$element->$field; that does the most damage. Looking at the products it is the text in the description which is making it slow, reducing the description to a couple of words makes it fast. This means that any product with multiple variations and large text, are slow to load, which is not great.