Mysql Two tables mixed data

I have two tables:

table1:

ID| Name
1 | firstname1
2 | firstname2
3 | firstname3

table2:

ID| Name
1 | lastname1
2 | lastname2
3 | lastname3

And i want insert combination table1 and table2 to table3 example: table3:

ID| Fullname
1 | firstname1-lastname1
2 | firstname1-lastname2
3 | firstname1-lastname3
4 | firstname2-lastname1
5 | firstname2-lastname2
6 | firstname2-lastname3
7 | firstname3-lastname1
8 | firstname3-lastname2
9 | firstname3-lastname3

A try in php (pdo) but is very slow... i must create 10 000 000 records (after combination)

my php:

<?php
//get firstnames, get lastnames before and...
foreach ($firstnames as $firstname) {
    foreach ($lastnames as $lastname) {
        $this->pdo->prepare("INSERT INTO `table3` (`fullname`) VALUES(?)")->execute([$firstname['name'] . '-' . $lastname['name']]);
    }
}

Soo, how i can create a query that mix data?

Thans