If you need to control mains AC loads, I highly recommend something like the Sonoff Wifi switches. They're similar to the wifi "Smart plugs" you can get these days but are aimed at fixed wiring installations and they're safety tested. You can also get versions with built in temp\humidity sensors in the switch, then re-flash the Sonoff firmware with esphome and control all 15 from a single raspberry pi running home assistant. This would allow you to set temperatures for individual rooms over the internet.