Performance affected by users ?

Hi,

We're currently trying to improve our response time for ProjeQtOr because for some of our collaborator's loadings are getting longer and longer.
As they're using it everyday it can be irritating so I started some investigations on the subject.

I did tests on the same PC / Browser connected on the same network.
For 2 accounts with the same profile (Admin), the ticket list is taking :
- For account 1 : 07.65s
- For account 2 : 18.64s
These values ​​can vary from about 1-2 seconds but the gap is constant.

So I'm here to ask you if you had an idea of what's the heaviest part on these loadings treatments.
The 2 profiles have an admin user profile, so they are loading equal number of tickets, maybe affectations or the amount of ticket they have created / worked on can have an impact on this ?

We're planning to do improvments on our web server too but I think there's a real relation between our accounts and the problem :
Months ago the problem was the same, so I copied the user of my collaborators (wich was encoutering slow loadings) and, the problem was gone. Now it's back ...

Is there anything we can do in the database either ?

Thank you in advance for your time and help,

Regards