On requirements review page I get:
PHP OPcode caching Not enabled
PHP OPcode caching can improve your site's performance considerably. It is highly recommended to have OPcache installed on your server.
I am on php 5.5.13 and it seems to have opcode caching builtin and turned on. Other sites (D7) on the server work
If I ignore the message and tell it to continue it installs. The status report contains the same warning message.