Hi Bawan,
Depending on your hardware it should definitely be achievable to handle 1.500 concurrent calls (3.000 legs).
This however sets up some demands to your implementation of freeswitch, i.e. you do not want 500 users accessing I/O-intensive operations like voicemail at the same time. And since FreeSWITCH handles calls in separate theads you want hardware that is capable of extensive multithreading. So I suggest going for hardware with as many CPU cores as possible and decent amount of RAM as FreeSWITCh is stateful (i.e. keeps track of conversations).
As Abdullah suggests it might be a good idea to equip your system with a load balancer. I can recommend using Kamailio with mod_dispatcher. It is easy to setup and lets you distribute the load across multiple FreeSWITCH servers.
For further advice You might want to equip us with further knowledge on the scenarios you want to use FreeSWITCH with.