Hello Krit,
The tenant is always yours, but you will share the whole system with other customers in a public edition. In a private edition the whole system with all tenant is yours. Of course this will add to the bill at the end of the month. 
But even if the system is under stress from other tenants it is still remarkable that the border is always 500.
I suggest to open an incident on the performance queue.
Sorry,
Horst