DHCP Design

Hi all, could someone help me with a DHCP design issue?
In my environment, I have 4 routers providing a Guest network for 15k users. To balance the load, all routers are in the same VLAN with DHCP enabled and the default gateway set to itself. In practice, the client will send a DHCP request and the server that responds first will be the gateway for the client.

However, this way, the clients are not balanced equally between the servers. Could someone give me an sugestion of ​​how to create a more robust DHCP structure that can better balance the clients?

Thanks