How to speed up my websites (backoffices)

like below fixes the issue What I will say in this answer is not specific to Kohana, and can probably apply to lots of PHP projects.
Here are some points that come to my mind when talking about performance, scalability, PHP, ...

Hope that helps memcached is a generic memory data cache. It's probably most commonly used to cache database objects, but it can accomplish a large number of other tasks.
The particular article you linked is describing how to use nginx in place of the Mongrel httpd usually used for the Rails web framework. memcached is being used to cache the results of dynamic pages that use querystrings to generate the dynamic content; in this specific use case, it appears the page will generate identical results with an identical querystring each time, so significant performance gains can be had by simply bypassing appserver generation and caching the rendered HTML in memcached.

I hope this helps . You are correct. "Instance" == Web Hosting Plan == VM. Settings like the pricing tier (Standard vs Basic), autoscaling, and usage quotas are all set at the Plan level and shared by all websites within that plan.
This relationship is a lot more intuitive in the new portal.

Hope that helps since I have not enough points to comment I'll just leave my thoughts here.
1) I would make the web app use the API for 2 main reasons:

hop of those help? I have use some tips like magneto catching feature, disable non used modules, merge css and javascript, disable system log. , There are setting in .htaccess file