First of all: is this problem now generalized? I mean all the client now get 30 minutes to load the application?? Or do you still have some clients that can load faster?
If you still have some client that can load faster, you can compare a log for your app on a slow client with one of a quick client.
If now all the client have the same problem, then this is on the server, meaning that some Windows Update may have been applied, or something changed that now take so much time to load.
The first thing to do is adding exclusion for the antivirus on the server to the path of the application and all the related libraries (like the .net Framework if it uses .net or Java if it uses java, or anything else) and the path for the database. May be just an update of the antivirus may have caused this, so I would also try without Antivirus at all.
Then if you can compare a quick and a slow machine I would slowly go through that process.. unfortunately it is a slow process because you have to compare all the dll load from the different machines and especially how much time it is taking.
If you no longer can compare, then we must assume something changed on the server, so uninstall all the latest update until the situation get back to normal.
Another great tool for this kind of problem is Windows Performance Analyzer... with that you can see the different timings for each operation quickly and easily that with Procmon because WPA was created just for that..
HTH
-mario