I would say no, a space blanket is not enough.

Add a wool or “disaster blanket” which are generally wool blends and are fairly cheap (under $10 USD). Use the wool/disaster blanket first, making sure to cover the head (with the face exposed) and truck of the body if there is not enough of the blanket, actually two blankets in an overlapping “T” pattern, with the top (which is double layered) of the “T” for the upper body works best and the space/mylar blanket wrapped around the blanked patient, acting as a vapor/wind/rain/etc. barrier.

If it is real cold, you can add a couple of towel wrapped heat packs (to prevent burns) under the blankets.

Pete