Biking in the snow with a trike is stable and fun in the curves! But since you are making 3 tracks instead of 1 or 1,5, your "rolling" resistance will be higher. The fastest in soft snow would be a racing bike: big narrow wheels. It will also be very fast in getting you in hospital... On hard packed snow a very wide tyre would be fastest. In real life, a studded tyre is the fastest ;)
Just enjoy it and take your time and you will be fine. I mean, a lot of people go far places and through a lot of trouble just to get repetiti-titi-titi-titit-ve excercise in a enclosed space (and many more don't), so no need to feel silly because you took a little more time to enjoy the scenery ... many people can't even best your average speed on a nice summers day...
Regards /Frederik - averaging 24km/h in the snow but then it's only 3km...