Change default 15 products per page on Category view

Goto Extensions in Extensions in opencart, Choose the extension type Theme

Click on edit button and change below listed value

For views change value from category.php from controller directory

	$data['limits'] = array();

			$limits = array_unique(array($this->config->get('theme_' . $this->config->get('config_theme') . '_product_limit'), 25, 50, 75, 100));

			sort($limits);