Crucible - migrate and upgrade from very old version 2.7.15 to current

[Daniel Matheis]

We are still running Version:2.7.15 Build:20120709053240 2012-07-09 of Crucible
and want to evaluate a migration and upgrade to current version (without losing old reviews)
Is there any guide? What I have found is

https://confluence.atlassian.com/fishkb/migrating-and-upgrading-fisheye-crucible-423298099.html

and

https://confluence.atlassian.com/crucible/crucible-upgrade-guide-298977392.html

The latter one starts only at Crucible 3.0 upgrade notes, so what about 2.7.15 to 3.0?

Any experiences?

Thanks in advance!

Daniel