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The 1.5.x branch of PrestaShop is latest the previous major version of PrestaShop, first released as a stable version in September 2012.
It has been superseded by version 1.6 in March 2014.
It's last version is v1.5.6.2, released in January 2014. There will not be anymore updates.
If you are still using version 1.5, you should upgrade to the latest version!
Documentation for PrestaShop 1.5.x
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