There've been reports of slow installs on kibana 6.2+. So far I haven't been able to reproduce on rhel7 and centos7 vm's but other users have.
Slow is roughly hanging for 1 hour+ on the install step. It should be taking less than a few minutes.
related,
https://discuss.elastic.co/t/unable-to-unpack-kibana-6-2-2/123736