I am new to Joomla and K2. am trying to take a site that is using Joomla 1.5.15 up to 2.5. it uses K2 v.2.2 I presume all needs to be updated including the template which it looks like is available in an updated version for 2.5 (Verdant).

I would like some guidance on the order of events to upgrade all these products without losing the clients work. most of his site content utilizes K2. have read about an extension available for the migration in Joomla but what about K2, does that get updated first or after.

please advise. any direction is greatly appreciated.

First BACKUP your 1.5 site......so you can restore it if necessary
i would move the akeeba backup jpa file to localhost and test the upgrade process there
You can use jupgrade from redcomponent.com or you can do it manually
This link may help getk2.org/documentation/tips-a-tricks/311-manually-migrating-k2-content-from-joomla-15-to-17

I would move the 1.5 site to the latest 1.6 version first
then install the latest k2 version and test to see if things work
then do the upgrade to 2.5 and reinstall k2 over the top