Back in 2015, we tried Prestashop with HHVM and it kind of worked. However, we noted even then that because of possible bugs you don’t need to move your shop from PHP to HHVM unless you have very good reasons. With the release of Prestashop 1.7, the argument for using HHVM became even weaker. Why?
Prestashop 1.7 is compatible with PHP 7, which in performance is similar to HHVM. Furthermore, HHVM has never been on the roadmap for Prestashop, while PHP 7 is now officially supported.
You can therefore expect to get sufficient performance using Prestashop with PHP 7 instead of HHVM, and you can avoid the added risks of using HHVM.