Alberto, sadly I do not grow any species of Agapetes but I know that they have several species in the Royal Botanic Gardens, Edinburgh, all under glass and certainly frost free, to the best of my knowledge, so that is not much help to you to determine what degree of cold they might accept. I would have thought from the forested areas where they are found in the wild, whether growing as epiphytes or on the ground, that they would get a fair measure of frost protection.
Fabulous plants that I would love to have space for... the markings on the flowers are wonderful, chevrons in delineated sections, looking like a cross between a fritillaria marking and a Crinodendron flower! But in most species the flower substance is not thich like a Crinodendron, though the appearance suggests that, they are not even fairly waxy/silky like rhodos or vaccinium, they are slightly papery... most unexpected. Another great part of the ericaceae... you are lucky to have this and it looks really good and a large specimen!