Hello,
We have made a few tests with your site. Your product page when our theme is activated without cache plugin – 1.82 s https://tools.pingdom.com/#!/bHcNu/http://arvven.com/urunler/ Your product page when default WP theme is activated without cache plugin – 1.45 s https://tools.pingdom.com/#!/bHcNu/http://arvven.com/urunler/
Your product page when our theme is activated + cache plugin – 513 ms https://tools.pingdom.com/#!/ej8w5n/http://arvven.com/urunler/ Your product page when default WP theme is activated without cache plugin – 398 ms https://tools.pingdom.com/#!/cb8F14/http://arvven.com/urunler/
So, if you sometimes get 16s I think it’s your hosting issues and you need to contact your hosting provider.
Regards
