Uploading images to Joomla under Ubuntu+Apache2+Nginx. How to clear memory?

Question

PHP

Intel(R) Xeon(R) CPU E5-2650L v3 @ 1.80GHz 1797.917 Mhz X 2
Apache 2.4.7-1ubuntu4.9
MySQL 5.5.47-0ubuntu0.14.04.1
PHP 5.5.9+dfsg-1ubuntu4.14
ISP manager
I ran into the following problem - when I try to load images, after the second or third visit to the site, I get an error in the logs for lack of memory.
I increased the memory limit for php execution, images are loaded, but the muscle began to fall.
Most of all, images don't free up memory. since there are many sites, and before the increase in the size of memory for php, it was possible to upload 2-3 images to each site. I didn’t give any more in any, or after a while, in any way.
Sites moved from another hosting. those images that were on the sites live perfectly there.