Extreme server lag and delay once the player count reaches above 16

Hello there,
New server here having trouble with some extreme delays and lag once our population reaches above 16. The moment it drops below 16 everything returns back to normal.
Any idea on where to start looking? Checked resmon 1 and no resource seemed to be a problem. Could it possibly be disc-inventory that we are using? the amount of import cars? We are really unfamiliar with issues such as this.
Thank you for your time.

Maybe take a look at this, see if anything turns up:

thank you so much, will be taking a look shortly