Induction heater MOSFET switch

I have one of these mini ZVS induction heaters that I use for heating my Dynavap vape (I have a script for weed so it's all good). I run it off a 3S DIY battery that I made with 30T cells and a BMS. When I read guides online about these, most say to use a 15A MOSFET switch. Currently the circuit I have goes battery > momentary push button switch > ZVS induction heater.

I get that it's hard to find a good, high current switch that's not really big, but this thing only draws 5-6A with a fully charged battery, and I only use it for maybe 15 seconds at a time so nothing gets hot (apart from the vape!).

I've been using it for quite a while as is and have been very happy with the performance. What's the real purpose of a MOSFET switch in this instance? Is it a safety thing to avoid a melted switch? I'm not sure how to wire up a MOSFET switch.