I've managed an upgrade from 1.5 5o 2.5 with PostNote. Couple of "lessons learned" that may help here.
1. It doesn't UPGRADE well. It INSTALLS on a fresh clean Joomla just fine. *I decided to completely re-implement the template.* Yes that means that I did reconsider using PostNote and changing to another template. Upgradability has been a weakness in previous Joomla versions, and this the design behind this template is not much different.
OK, if you're still reading and not just flaming me for the previous comment, here are some more thoughts related to upgrading PostNote.
2. Related to #1, it seems that there are template positions on the home page in 1.5 that simply weren't in the 2.5 version of the template of they were in different places (user11-20 as I recall). So stuff got "lost". This is further complicated by the fact that I am not constrained to use "valid" module positions in Joomla, meaning it was not clear why a given position didn't work. When I studied the position placements in PostNote 2.5 very carefully, it became much more clear what was going on.
3. After I ran jupgrade and went to the new site, I never could see the PostNote template until I did "discover". But even after I discovered, it didn't work. On to the next point.
4. If PostNote was installed in 1.5 and you upgraded to 2.5, you couldn't easily uninstall PostNote. Basically I couldn't "panic" and try to "do over" once I realised I had the problem. I had to use SQL to delete the PostNote rows from __template_styles table and then delete the PostNote directory from the Joomla template directory. (note: I needed to make another template the default before I did that!) Then I could install the 2.5 PostNote template and get around to completing the upgrade/reinstallation.
5. The template configuration has a new and, in my mind, MOST silly automation that keeps popping open when you hover over it, resizing the text and fields all the while. It makes using a 1024 x 768 display almost impossible. Another instance of usability that Gavick overlooked. They seem to have designed this for HD wide screen displays.
A couple of other tips, not related to PostNote, but worth knowing as you start down that road.
1. I studied the posting in
https://www.gavick.com/forums/postnote/ ... 14020.html
as it seemed to related to my situation. It may be helpful to read through that, but don't be too frustrated when you start. (I'm in software support too, and found that interchange most interesting and somewhat entertaining, but I digress.) What I finally decided there is that Gavick never intended this template to be an upgrade, unfortunately they didn't make it easy to figure that out too.
2. The 1.5 jupgrade module only seems to upgrade "core" modules. Unfortunately Joomla has a "custom" and a "mod_custom" module type, and only the "mod_custom" upgraded. I found that by using SQL to modify the module types that were "custom" to "mod_custom" that they came across with no issues. Your mileage may vary. jupgrade can be configured to drop the target tables, so there is a form of a "do over" there.
3. I'm a K2 user and the previous point means all of the modules related to K2 needed to be manually rebuilt. Menu's too, but once K2 was installed, it was simply a matter to open the item and hit save. There are other threads about this, but in my simple site, that approach was the fastest. YMMV
Best wishes to others that embark down this road.