SenseNet - performance issues during files insertion or deletion

Question

I have Sense/Net 6.5.4.9243 installed on prem. It works as a simple documents archive - people are inserting things there, others are downloading, from time to time there's a need to delete some file.

SenseNet's IIS app is on the same machine as the 'main' app, also the database is on the same machine as the app's database. SenseNet's files are being manipulated via .NET client only.

The problem is that I'm facing some performance issues during

• insertion of large files i.e. >10 MB
• files deletion

The symptoms are that during peak hours, insertion takes up to 2 minutes and often ends with with the following exception:

SenseNet.Client.ClientException: Error during binary upload.
System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host

When it comes to deletion, it also takes long time to finish (>1 min), but it succeeds, I found no logged exceptions.

There's no problem with downloading at all, it works like a charm.

I checked the resources on both machines (app and database) and it seems like everything's fine. CPU is idling, some memory left unused, there's no excessive disk I/O.

Is there a way to see what causes such problems? How can I fine tune the SenseNet's database or IIS hosted app to speed up these two processes mentioned above?