internal data

Hello, I've a problem with the disk space used by xenforo. Internal_data folder is 12GB. Can this be a normal size for a forum with 900'000 messages? We can't change server/upgrade disk space, so I have to try to limit the size of this folder. Any idea? Thanks.

When i see the internal_data/temp folder, its size is about 3gb All files starting with xf....... bdas3_...... Also, some files ending with .temp Files creation dates are different and old mostly. Files looking from 2014 year or like february 2015, august 2015. And my question is, can i...