it actually depends on where you live, time available, training objectives, etc.
But I cant see what is the benefits of riding the trainer at such low intensity. Burning fat is not a valid point, if someone wnats to lean down, the answer is simply burn more calories. Burning calories is done via workload, you're better off riding tempo intensity, that way more calories are burnt.
I guess most people riding the trainer are time constraint people, hence why I dont find any argument in favor of L2 riding. There are specific adaptations (heart contraction, efficiency) to riding this intensity but like I said, I would not bother with these during winter time.
Again, winter is relative. Winter here means its dark at 3h45pm, road full of snow/ice/salt and impossible to ride safely outside.
Given the OP sound quite new and wants to loose weight/build a base, I'd recommend lots of L3-L4 intensity work. Building base with L2 is an old school outdated principle, especially for amateurs who dont have 20-30h available to train each week.