PHP Fatal error: Allowed memory size of

Hello,

I am getting following error on any target/contact deletion.

PHP Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 1126400 bytes) in /var/www/crm-dev/crm/vendor/zf1/zend-search-lucene/library/Zend/Search/Lucene/Storage/File/Filesystem.php on line 163

Configuration:
ubuntu 20.04
8 core , 16 GB RAM
256mb php_memory_limit
CRM Version 7.12.4

Total DB 14 GiB
aod_indexevent 700 MiB
campaign_log 3.7 GiB
emails_beans 4.8 GiB
emails_text 900 MiB
email_addr_bean_rel 445 MiB
prospects 650 MiB
prospect_lists_prospects 370 MiB
securitygroups_records 850 MiB

Grateful for any ideas & help
Thanks a lot