Piggies are most comfortable between 18-22 degrees, but below 15 is chilly for them.
What is also important is not exposing them to sudden and extreme changes and fluctuations in temperature - if they are normally kept indoors, not in the conservatory, and the room they live in is, for example, 18 degrees, then going out to a 10 degree conservatory would be too much of a difference for them.
If they live in the conservatory all the time, then obviously they are not exposed to a fluctuation from coming from a warmer room, but living out there in 10 degrees would be considered too cold and additional measures would need to be taken to ensure they are warm enough. If you don’t have heating out there, then measures would need to be similar to those for outdoor/shed dwelling piggies - insulation, blankets on the cage (if you are using an indoor cage then keeping them warm is harder so covering it to ensure draughts aren’t getting in and any warmth is kept inside as much as possible), insulation, a hay filled cage to snuggle into. Perhaps also using an oiled filled if possible radiator to warm the conservatory up.
