Im trying to create several users for customers by executing a wizard from a transient Model, im creating about seven hundred users but my methods are taking too much time to complete only with one hundred. Can anyone help me to improve my methods, actually are this:

@api.multi
def create_student_user_selected(self):
    customers_ready = 0
    active_ids = self.env.context.get('active_ids', []) or []
    records = self.env['my.customers_model'].browse(active_ids)

    for customer in records:
        customers_ready += 1
        print('customer number '+ str(customers_ready))
        if customer.email and not customer.usuario_id:
            self.create_customer_user(customer)
        else:
        print('The customer has no email')

@api.multi
def create_customer_user(self, customer_id):
    customers_group = self.env.ref('stock_sales.customers_group')
    user_data = {
        'name': partner_id.name,
        'login': partner_id.email,
        'partner_id': partner_id.partner_id.id
    }
    user_customer_obj = self.env['res.users'].sudo().create(user_data)
    partner_id.sudo().write(
        {
            'user_id': user_customer_obj.id,
        }
    )
    customer_id.partner_id.email = customer_id.email 
    customers_group.users += user_customer_obj