PUB/SUB+PUSH/PULL Messaging Broker - How to improv

Question

I have implemented this ZMQ Client-Server architecture with the order to one message from Sender client, this message arrives at other clients Receiver 1, Receiver 2 and Receiver 3.

This means that the all receivers can see the same data from Sender

In this architecture, I have python clients and c++ clients. The server is coded with Python using pyzmq binding.

The question is: Why on my python clients the message appears faster than on my c++ clients?

Is this related to the fact that the server was coded in Python?

What kind of non-functional considerations should I have, so as to improve the performance of the messaging system?

Is possible think in one thread by each message routed to the receiver?

I would meet your considerations about it