Multicast data overhead?

Multicast data overhead?

My application uses multicast capability of UDP.
In short I am using java and wish to transmit all data using a single
multicast address and port. Although the multicast listeners will be
logically divided into subgroups which can change in runtime and may not
wish to process data that comes from outside of their group.
To make this happen I have made the code so that all the running instances
of application will join the same multicast group and port but will
carefully observe the packet's sender to determine if it belongs to their
sub-group.
Warning minimum packet size for my application is 30000-60000 bytes!!!!!
Will reading every packet using MulticastSocket.receive(DatagramPacket)
and determining if its the required packet cause too much overhead (even
buffer overflow).
Would it generate massive traffic leading to congestion in the network
because every packet is sent to everyone ?