The warning is based on percentage of System mem left and the percentage is not that low as far as I recall. (90% ?)
It says it in the message "You
may experience..." If you do not encounter any other problems and if the scene still renders as fast as ever, than you can ignore it.
It serves as I reminder, that if you push onward and beyond your RAM amount, you will encounter paging, which will kill all performance.
However, do you happen to have dual Xeon? Is that what you mean by 16+16?
Then there are two modes for memory, SMP and NUMA. One allows to share memory and the other one doesn't. If it is in non share mode, than you only really have 16gb. I am not sure how this plays with Corona, as I have no idea how it works.
If you have performance drop, then state so and someone with dual xeon experience will have to answer this.
Prime User for questions like this is
Juraj_Talcik, who is the moderator of the Hardware subforum.
If you have no performance drop, ignore the message and know, that you will soon reach the limit.