Optimizing the script to reduce the consumption of RAM

Good day for everybody.

Recently encountered a problem, WordPress 4.8.5 + PhotoGallery Ecommerce, as the site became heavier with time, then when I try to download the heaviest albums with a photo, it gives an error of “Allowed memory size of 268435456 bytes exhausted (tried to allocate 119975936 bytes) in / home / supers06 / supersprox.eu / gallery / wp-content / plugins / photo-gallery / admin / views / BWGViewDownload_gallery.php on line 32 “- which indicates that the script does not have enough RAM memory. On the server php_memory_limit: 256M and increase unfortunately on this server is not possible, but I already tried to move website to more powerful server, then another problem arose, all the albums are downloaded even the heaviest ones, but the downloaded archives are empty, and when this archive is opened it give an error “The archive is corrupted or has an unknown format”.
I consider both options as optimizing the script on the old server to reduce the consumption of RAM and also fixing the problem on the new server.
Tell me please, who has any ideas?

Thank you very much in advance !

The page I need help with: [log in to see the link]