Optimizing site performance on CMS Joomla 2.5 in ubuntu server 14.04.1?

Question

Joomla

Essence of the question: experience with linux at the level of a regular user, maybe a little higher.
At work, they demanded that LAMP be installed as a "Unix admin" for the portal to work on Joomla 2.5.
The portal is handled by a separate programmer. My job is to make it work.
Now there are complaints that the site began to slow down. The free command says that on a virtual machine from 488M 30M is free, the swap is used from 800M, 200M is occupied. And now he is unloaded.
I understand that it swaps and slows down, the virtual machine is hard to work with disks.
Question: tell me the algorithm for identifying bottlenecks, preferably with more specific examples.
And also, if possible, then the solutions depending on this.
Now I'm looking at:

1. read about the optimization of Joomla.k. maybe she's slowing down.
   
2. try installing lighttpd instead of apache
   
3. It is possible to add nginx to apache - now bare apache+Joomla
   
4. Try to optimize apache + mysql configs - but I have never encountered this
   

PS I work in a government agency (university), so hiring a person from the outside for money is not an option.

Answer 1

1. Joomla can and should be optimized - this is the task of the programmer who deals with the portal. When mistreated, this CMS slows down not like a child (however, like everyone else).
look first of all:
- enable caching
- enable G–Zip
- optimize the number of installed plugins
- check the layout of the template (number and size of images, manually written sql queries, etc.)
- perhaps a plugin like JotCache, JCH Optimize will save the situation , RokBooster - put one thing, carefully check css and output scripts. These plugins compress and merge the rendered files, increasing performance.
Read on the topic:
speedupyourwebsite.ru/books/speed-up-your-website
speedupyourwebsite.ru/books/reactive-websites
www.tumencev.pp.ua/programming/cms-joomla/joomla-a...
baddyblog.ru/uskorenie-sajta-na-joomla
2. General advice:
- connect CDN - for example , CloudFlare
3. Server optimization:
- nginx is a good idea. I had it right away. It's also a good idea to immediately register caching of pictures and everything else.
- apache configs - I don't remember, I don't think I touched it.
- optimize MySQL - set up indexes and check with the mysqltuner utility
- periodically clean up the jos_sessions table
Read here:
firstwiki.ru/index.php/%D0%9E%D0%BF%D1%82%D0%B8%D0...
max- joomla.ru/uroki/92-htaccess-dlya-joomla-pravil...
habrahabr.ru/post/108418
The process is painstaking and thoughtful. In my case, as a result, the most effective measures turned out to be: editing com_content (removed the check for the creation date), installing the JotCache component + enabling caching, setting up nginx caching, tuning MySQL and client-side optimization of images, scripts, etc.
Good luck!