Most of us are not wearing special clothes made for riding in -15c.
I'm wearing my BMW Street Guard, but any good quality suit is ok. But it must be too big for you in a hot summer day, so you can wear 2-3 layers of thin wool underwear too. Wool on your skin, all your skin, from toes to ears, and on your head too if it is really cold.
And I wear two wind stopper neck.
The problem is the feet.
I'm riding a sidecar so I feel it is OK to wear normal boots, boots not made for riding a mototbike, with protections.
My favorite is Muckboots. Thay are waterproof too. And yes, you never know if you need that!
If I was riding a solo bike I would not know what boots to wear.
But again; too big for you in the summer, and wool (only wool!) socks. Not too many socks; you need room for moving your toes, that help too.
And we have Gerbing electric clotes.
I have socks, and they help a lot!
And I have gloves too. But muffs (is that what you call the 'bag' on you handle bars?) and electric heated handle bars, together, help much too.
Some of us need all this, and more. Some need less.
Sometimes it is only -5c, and that is not cold.
But I remember when I rode to Lom in 2009: It was below -25c for many hours, and that was cold. But I managed because I was wearing my homemade fur coat. That helped a lot - that saved me!
If you struggle to put enough wool under your riding suit, wearing a sheepskin coat help.
If you are moving much (= falling off the bike, or playing) you won't feel so cold, and then you might not need it. But in -25c I guess we all would love to wear something extra, like a coat.
I'm sorry my english is so bad.
Please ask more, if you want to know more! Please do!
Do you still want me to find links for clothes?

Liv.