Hello Nolly and welcome to the forum, I had a quick look at sims and found the following:-
Just looking at the size of Pulsar.exe
Open Sims 1960k
1 student search 47,592k after search is closed
Open and Close Nova T and do another student search 47,736 k
Open and close student search - no search done 49,484k
Open and close Report designer - do nothing 59,996k
So as far as I can see just opening and closing things in Sims would increase it's memory usage. What actually causes this you would need to ask the people who designed it, perhaps it is loading part of a database and not releasing it again but it certainly appears a bit on the sloppy side.