<?php
$order = Mage::getModel('sales/order')->loadByIncrementId($this->getOrderId());
$totall = $order->getGrandTotal();
?>

<?php $objectManager =  MagentoFrameworkAppObjectManager::getInstance();
          $orderData = $objectManager->create('MagentoSalesModelOrder')->loadByIncrementId($block->getOrderId());
          echo "<pre>";print_r($orderData->getData());
    ?>

$block->getRealOrderId();

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <preference for="MagentoCheckoutBlockSuccess"
                type="VendorModuleBlockCheckoutSuccess"/>
</config>

<?php
namespace VendorModuleBlockCheckout;

class Success extends MagentoCheckoutBlockSuccess
{
    /**
     * @return int
     */
    public function getGrandTotal()
    {
        /** @var MagentoSalesModelOrder $order */
        $order = $this->_orderFactory->create()->load($this->getLastOrderId());
        return $order->getGrandTotal();
    }
}

<?xml version="1.0"?>

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="Vendor_Module" setup_version="0.0.1" />
</config>

<?php
MagentoFrameworkComponentComponentRegistrar::register(
    MagentoFrameworkComponentComponentRegistrar::MODULE,
    'Vendor_Module',
    __DIR__
);

php bin/magento module:enable Vendor_Module
php bin/magento setup:upgrade

$block->getGrandTotal();