Third world trying to decide

Hey fellas~!

I managed to gather some $$$ and I want to upgrade my phone. I currently have a TCL NXPAPER 40 and I hate it - the way it runs, the camera, everything.

Thing is, I know nothing about Apple. I don't have the cash for a brand-new/latest model, but I was thinking about getting an iPhone 15 or 15 Pro (which gets me hesitant, as only used models are available here in my country, and boy do we love a good scam down here). Is that a good choice? Should I wait and save for the 16 instead? And is 6GB of RAM on the 15 too little?

Thanks in advance!