Large number of folders slows down Webapp?

[passt]

Kopano 8.7.16

I have a user who has hundreds of mail folders in his mailbox and who uses the Webapp. It happens to him very often that with almost every action, such as writing a new e-mail, the browser shows a warning message ‘webpage not reacting’.

Is it possible that this large amount of folders can be blamed for it?

Peter