My experience with pepper plants is that won't do much unless it is warm enough, but once they are warm enough, it is light they crave.

I tried growing rocotos (Capsicum pubescens) this year. Everything else I grews was pretty crap, but the rocotos did stunningly well, and are quite the hottest chillies I've ever grown. They have a reputation of being more cold tolerant than other chillies. I grow my chillies outside in containers against a sunny wall, so cooler than yours, but maximising the light.