Performance are worth and worth. It seems ProjeQtOr is using a large amount of the memory of the server.
What di you call large amount ?
It may use 100% on 1GB, sure...
What is important it to dimension the server correspondong to usage : CPU, RAM, disks, ... and not only monitored "one shot" but followed to identify hights values.
The worth is Imputation. It can take more than 1' to save the week.
Timesheet is one of the "heavyest" screen to manage.
IT has be improved over time, and it will now be difficult to improve it without a complete refactor.
Performance will depend on number of lines to display.
Less than 20 is quick and fluent.
Up to 100 is slower but still easy to use.
Over 100 lines, performance may be bad : but is it really a good design to work on hundreds of activities in parallel.
Possibly you may close finished activities, and use options to hide ununsed line (not started on finished)