Redirect URL for subdirectory not working

I’m pointing my website’s URL to a subdirectory folder name “2015”, but now every URL in my header navigation are pointing to the index/home page, in regardless if it’s /about or /contact.
Here’s the website: https://www.funyearart.com

I checked my setting in wordpress backend, WordPress Address (URL) is set to https://www.funyearart.com/2015, and Site Address (URL) is set to https://www.funyearart.com.

My .htaccess as follows:

# Use PHP5.4 as default
AddHandler application/x-httpd-php54.php
RewriteEngine On
RewriteCond %{HTTP_HOST} ^(www.)?funyearart.com$
RewriteRule ^(/)?$ 2015/ [L]
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

I don’t know what I’m doing wrong, but if I redirect the URL back to /2015, and reset and .htaccess, it pages went back to normal but with /2015 in the URL.

Any help is much appreciated, thank you.