Overwintering of Premna

Hello,
I would like to ask those whose native plant the Premna is, or those who grow it for more years. How conditions does it need to overwinter succesfully? I live in Europe, in the part with cold winter, so I cannot overwinter it outside. What temperature is optimal for it please? I have it in an ordinary room near the window with temps over 20, but I am afraid it doesnt like the dry air from floor heating. I have the possibility to overwinter it on the window in the room with no heating with tems to 15 °Celsia. Would it be better or should I keep it where it is for this season and try the colder place next year?
Thank you very much.
Regards,
Zuzana

It doesn't like cold weather and will die if frozen. I grow mine outside but Ive heard reports that it doesn't do well indoors so perhaps you should considered some other species.

If it is small, you can put it in an aquarium (works like a greenhouse) where humidity can be increased and can be placed indoors. You can also artificially light it with grow lights (6500K).

Thank you for the advices, I hope it will stay alive during the winter where it is now, and when the weather will be hot enough it will go out with other bonsai. For now, it is still green, and has the new shoots, so I hope it will prosper. But I will think about adding the lights and wetting the air.
Thanks.

If you are really in a bind, you can also put a clear plastic bag over the foliage. It will help keep humidity up for the leaves.