The way your doing your form entity field and collection is bad and your performance issue may come from this.
First try to remove the queries you write in your forms, this is not the proper place especially with your queries which are the default one so no need to override them.
So you can do very simply like this :
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder
->add('ref', 'text')
->add('title', 'text')
->add('lessor', 'entity', array(
'class' => 'MyCompany\AppBundle\Entity\Lessor',
'property' => 'title')
)
->add('type', 'entity', array(
'class' => 'MyCompany\AppBundle\Entity\ObjectType',
'property' => 'title')
)
->add('prices', 'collection', array(
'type' => new ObjectItemPriceType()
))
->add('values', 'collection', array(
'type' => new ObjectValueTextType()
'allow_add' => true,
'prototype' => true
))
->add('save', 'submit');
}
Learn more about entity form type here
If you need to pass some choices like it seems you want to do, you will have to set the query_builder option and give it a repository method (Example here), this is the correct way to do.
For the collection, you have a full example in the cookbook, I hope it will help you.
If it does not solve you problem, try to setup xhprof, it will give you a more detailed graph of your request and why it takes so much time : Xhprof bundle