The 1.5.x branch of PrestaShop is the previous major version branch of PrestaShop, first released as a stable version in September 2012.
It has been superseded by version branch 1.6 in March April 2014.
It's Its last version is v18.104.22.168, released in July 2015. It will only receive security There will not be any more updates.
If you are still using version branch 1.5, you should upgrade to the latest version!
Documentation for PrestaShop 1.5.x