Comment # 8 on bug 993516 from Donald Curtis

The workaround "set DHCLIENT6_MODE=managed in ifcfg file" didn't change
anything (in my case).
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But, taking points made by Nirmoy I checked the contents of
/etc/sysconfig/network/ and made the following changes:
 - In "config" decreased WAIT_FOR_INTERFACES from '30' to '8'.
 - In "dhcp" made the following changes:
 * DHCLIENT_RELEASE_BEFORE_QUIT and DHCLIENT6_RELEASE_BEFORE_QUIT set to "yes".
 * DHCLIENT_WAIT_AT_BOOT and DHCLIENT6_WAIT_AT_BOOT decreased from '15' to '4'.

Additionally I commented out an extraneous DHCLIENT_SET_DEFAULT_ROUTE='yes' in
ifcfg-enp2s0.

The DHCPv6 lease is now committed 4 seconds after the Ethernet interface is up.
And, the wicked service is now taking only 6.610s at boot.
I'll attach the filtered Journal from this boot.
 ** I'll add a comment to Bug 975933.