C5-8.2.1 Site faster with PHP v5.6 and server cache off

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How could it be that the site runs faster on PHP v5.6: 3-4 sec vs 10-15 sec on PHP v7.1 and apache cache turned off in php.ini:
opcache.enable = Off
xcache.cacher = Off
register_globals = Off

Something's not quite right here.

PS. all caching is on except for full page caching.

linuxoid