Magento 2 add to cart performance issue

In my magento 2 website adding to cart takes about 10 sec. Caching is OK. Redis is configured. Merging/minimizing for CSS/JS is enabled. I’m notised that after first adding item to the cart , adding to cart of this item takes few seconds (Looks like caching), but after 5 minutes it’s takes too much time again. Maybe there is way to redute time or cache “add to cart” for a long time ? Great thanks and sorry for my english.