Searching in categories AND custom fields

Adding the tax_query parameter to the $args array with the proper arguments will check for the category as well (untested):

$args = array(
    'post_type' => 'product',
    'posts_per_page' => 15,
    'paged' => $paged,
    'meta_query' => array(
        array(
            'key' => 'meta_easyfatt_libero_1',
            'value' => 'Men',
            'compare' => 'LIKE',
        ),
    ),
    'tax_query' => array(
        array(
            'taxonomy' => 'product_cat',
            'field' => 'name',
            'terms' => 'Clothing',
        ),
    ),
);