For My Next Substantial Posting...
Let us assume that the portal led to a community. You are now a child of 15 with a ton of stuff you thought would be important, in the middle of a village, town, or city. Let us further assume the disembodied voice arranged for somebody to be there to greet you when you arrived. You're in like Flynn, right?
Wrong.
As far as people can see you are 15. You look 15, you act 15, you have the understanding of a 15 year old. All those books you brought along with you? You may not understand them. The knowledge you retain from your older self? You may not understand that.
In addition, you have no experience with the world you now find yourself in. You may now certain important people, but you don't have even the basic knowledge of culture and society even a child of five would have. And you may not have the chance to learn.
What will the locals see? A child. Certainly lost, possibly abandoned. They will be puzzled mightily as to how any child of 15 was allowed to come through a magical portal on their own, likely ignoring anything you or the voice have to say about how you were once a full grown adult. You look like a kid, you must be a kid.
Guess what? You 've now got a guardian, and that's if you're lucky. (The alternatives will be dealt with in later installments.)
A new guardian, possibly even a new mom and dad. In a culture that knows nothing of civil rights, equality, or even enlightened child rearing. You try asserting your "God Given" rights you're likely to get a good backhand. Maybe even a thrashing. Dad (or whatever title he holds) runs the show, and you have no say in the matter. Want to worship an evil god? If you have any sense at all (and even 15 year olds have some sense), you're gonna drop that idea. Might take a beating from your new foster parent, but you will drop it. Or you may very well die.
The stuff you brought with you? It's no longer yours. At best 'dad' will now own it. At worst the authorities will confiscate it; gathering sages and scholars to study it if you're lucky, destroying it if you're not.
Which could well mean being questioned by the authorites about yourself and your stuff. Which may not be at all pleasant.
In short, your introduction to your new world, even under the best of circumstances, need not be a pleasant one.
Next up, How Your Introduction Could Be Worse