<?php

$item = array(
    'phone' => array(
        array(
            'Item' => 'S5',
            'info' => array(
                array('seller' => 'John', 'price' => 1800),
                array('seller' => 'Mason','price' => 1200),
                array('seller' => 'Alex','price' => 1500),
            ),
        ),
        array(
            'Item' => 'iPhone 5',
            'info' => array(
                array('seller' => 'Depay', 'price' => 1900),
                array('seller' => 'David', 'price' => 1450),
                array('seller' => 'Daemon', 'price' => 1600),
            )
        ),
    ),
);

 foreach($item['phone'] as $key => $price) {

        foreach($price['info'] as $info => $price2 ) {

            if ($price2['price'] >= 1500) {

                unset($item['phone'][$key]['info'][$info]); 
    
            }
        }
    }

echo "<pre>";
print_r($item);