I have this kind of lab environment. My SMS is a VM on ESXi (HW: HPE DL380p). Gateway is a Check Point appliance. The model is not relevant here. Core switch is Cisco 3750. ESXi enables me to test different scenarios with Identity Awareness for example by installing a Windows Server etc. and Cisco to run several testing environments parallel.
Cisco also works as my DHCP-server issuing IPs to my lab wifi. This is kind of cool because it allows me to connect to my lab from my bedroom using a phone or pad. I've been planning to add a small console router as well, so that I wouldn't have to run to the garage when a serial connection is needed.
In your case you could build something similar having the 15600-cluster in the middle as your main firewall. I don't have two similar appliances, so I'm only running a single gateway (model depends on whatever I have available usually 4K or 5K series). I can set up VMs with clustering if needed.
What comes to SmartConsole, I can run it on any windows computer or VM connected to my lab wifi.