Overwinter commercial-type store lambs on hay and 1/2lb 16% feed (suitable for males if there are any wethers in the group) per head per day, yes. Provide shelter from the worst of the weather, of course. Watch feet if they spend a lot of time on the same ground - try to keep the ground clean, move things around, use lime, etc.
But if they're as good as ready for slaughter in Oct/Nov then you made the right choice
Primitives will typically need two summers to be ready for slaughter, so if you got some next summer you'd keep them around 12 months. They would also winter better and grow away more strongly come the spring if they get a little cake and some hay. I give mine 1lb cake between 3, plus a bit of hay.
I feed hay at a rate of 1 small bale between 60 primitives or 40 commercials per day. If they're clearing up every wisp, I up it a bit. If they are leaving some, I decrease it a bit. Hay is best fed in two feeds, if you can.
If we get another freeze/snow, they'll eat - and need - quite a bit more, up to twice the above, while the ground is frozen and/or covered.