Change vagrant php starting version
Well i am not sure as i didn't used php5 for homestead or changed but this could help you.
If you look folder Homestead that you cloned from git this url :
git clone https://github.com/laravel/homestead.git Homestead
In this directory you can find directory called scripts
.
In script you can find file with name : serve-hhvm.sh
you can edit this file in any editor like vim or sublime and change php path here then :
vagrant reload --provision
There is also a file called serve-laravel and this file have all settings related to laravel and path for php7 fpm file sock :
fastcgi_pass unix:/var/run/php/php7.0-fpm.sock;
I hope this should fix your issue.