Hello Clemens,
Thanks for the added info. It may be acclimating to the new set-up, though I notice your soil may need to be a bit more grittier, try to add more pumice or perlite to allow more air in the root zone. It can certainly take much more sun in your area and your temps are so good, since you will have better humidity conditions too than what we have here. Try to check the condition of the roots too, for some reason it is unable to drink, so it manifests it by dropping leaves.
There is hope for the plant, seems the trunk and remaining branch looks firm, so if above part is okay, then check below soil level.
