The car is company owned rather than leased. But you're right, changing them might potentially cause issues for the TPMS. Having checked, it looked like the only option for changing the wheels and tyres would be to use 17 inch rims and deeper profile tyres. All the companies who sell wheel/winter tyre packages seem to recommend getting authorisation from the vehicle manufacturer before fitting. It's just too complicated for something that will only really be of benefit for a couple of months at best.
Besides that, if I was the only one able to get anywhere in snow, I'd be expected to pick everybody else up!:-)
Alan