2 CPU and 6GB RAM

Will be quite enought for about 10 simultaneously connected users.

I feel that the diary and some tabs are slow

How must is slow ? 3s, 5s, 10s, 10mn ?

How can I increase the performance? Is it possible to change any parameter on php.ini or other parameter to increase the preformance?

There are many ways to increase performance of a PHP application like ProjeQtOr, but the subject is out of scope of this support forum. We can provide technical support through assistance service. Request for a quote on the Contact form if you're interested.

Hints :
Watch for spinner : when it stops "turning", it means response has been received from server and your PC is working.
If it is the local treatment which is long, use a quicker broser (give up with IE, try Chrome).
If you look at the browser console, you'll see for each page request the logged time spend (total / server side / client side).

2 CPU and 6GB RAM

Will be quite enought for about 10 simultaneously connected users.

10 simultaneously users : doing something as recalculate planning, create projects... not just connected?

I feel that the diary and some tabs are slow. How must is slow ? 3s, 5s, 10s, 10mn ?

Aprox. 9 sec to display the diary of a ressource which is full on the current month (full on affectation)

Hints :
Watch for spinner : when it stops "turning", it means response has been received from server and your PC is working.
If it is the local treatment which is long, use a quicker broser (give up with IE, try Chrome).
If you look at the browser console, you'll see for each page request the logged time spend (total / server side / client side).

Thanks for the hints, it was very usefull.