Since, for sentences.

[ElectricPulse]

I am from slovakia and I have taught myself english through watching videos, films and everything that involves the internet. Even tho its pretty clear that I have no problem with the language, at school I still get challanged by teachers who bring up weird rules about the tense and what tense in what sentences should I use. Unfotunately I am no match to the grammar rule generator that is my teacher and thats why I cant argue with her. She can always just say 'thats incorrect bcs ...., maybe u have heard it from american films'. Which is a infuriating response for me, like I said I have been learning english since like 6 or 8 - partly bc of my older brother who always shamed me for not going to the cinema with him to watch movies bc I didnt want to listen to english films. Even tho I have a *slavic* accent and I often mistype words, I still have no problem with the actuall language. - Thats the long backstory, now for the actuall question. In sentences with since and for is there rule that u should always use present perfect - I have worked there since 2015 - . And is a sentence like this - I worked there since 2015 - a gramatically incorrect sentence. Like I said grammar is my weakness bc I frankly cant give a ~ to bore myself with rules that dont teach me anything and dont help with my accent or with my backwards translation. Where I derive words not from my native language but from English. Thank u for your help!!!

[darcy]

If you say "I worked there since 2015", you will confuse your listener. That's because I worked means it's past, it's finished, you don't work there now. But since 2015 means from 2015 to now: you do still work there now. So you are contradicting yourself.
Grammar rules have purpose: they help you to communicate more clearly.