I've just extended my subscription and I can no longer find the donwload for Joomla 1.5
I am afraid to understand that Cook no longer supports it ? Is that true ?
I have parsed the forums but I found no topic about that point.

Yes exactly.

Because there are too many differences.

1.6, 1.7, 2.5 will be compatibles for very long time in future. And even cross-compatibility, wich means all these versions together.

It is maybe a problem for a lot of users, but for Cook it is better because it will not instanciate strange deprecated code.

MVC structure is really different on 1.5 and I don't want double source.
For improving the service, it was a nightmare.

By the way, support for 3.0 is on the way...

I perfectly understand the reasons why.. but just please at the subscription time you MUST advert the user by a clear dialog or screen that Joomla 1.5 support will no longer be supported.
Now I am going tu upgrade my site ... to 2.5