Hi @benjamin.nussli,
welcome to the forum, it’s nice to have you here 
One question regarding your statement: Does this also happen when you initiate a new conversation? I ask this question because for GPT3 the whole content of the conversation was re-submitted when you posted a new message. So the deterioration in performance might also be related to a increase in needed computing power because the more content is submitted the harder it becomes to answer the messages.
Can you provide some further details on when you are experiencing the performance issues?