How to combine this two "if" conditions?

With this code i get the last 3 posts that contain "solar-signs-related" tag on the custom post "product" page that have "solar-signs-streetscape-elements" term.

But how to combine two "if" so it will display also the blog posts that have "interior-system-related" tag if the custom post "products" page is "interior-systems"?

if ( has_term( 'interior-systems', 'categories' ) ) {
  $args = array(
  'post_type' => 'post',
  'showposts' => 3,
  'post__not_in' => array( $post->ID ),
  'post_status' => array('publish'),
  'orderby' => 'date',
  'order' => 'DESC',
    'tax_query' => array(
     array(
    'taxonomy' => 'post_tag',
    'field' => 'slug',
    'terms' => array('interior-systems-related') )
    )
);
}
if ( has_term( 'solar-signs-streetscape-elements', 'categories' ) ) {
$args = array(
  'post_type' => 'post',
  'showposts' => 3,
  'post__not_in' => array( $post->ID ),
  'post_status' => array('publish'),
  'orderby' => 'date',
  'order' => 'DESC',
    'tax_query' => array(
     array(
      'taxonomy' => 'post_tag',
      'field' => 'slug',
      'terms' => array('solar-signs-related') )
   )
 );
 }
$query = new WP_Query($args);

if ($query->have_posts()) : while ($query->have_posts()) :       
$query->the_post(); ?>           
<div class="post-wrap relat relatblog">
<h2 class="entry-title"><?php the_title(); ?></h2>
</div>                   
  <?php endwhile;
  wp_reset_postdata();
  endif;
  endwhile; ?>