😄🤣😄

Uly, back to Past Perfect tense ))
Is this correct to say?
I was waiting for 15 minutes but no one had joined the meeting.

If so, how the meaning will change if we skip HAD?

No, because it sounds like they hadn’t joined BEFORE you waited.

I WAITED for 15 minutes, but no one joined the meeting.

The above sentence is clear - Simple Past Tense.
But what if I was to start my sentence with:
I was waiting...

I was waiting for someone to show up for the meeting, but after 15 minutes, nobody came.

As for the Past Perfect, I like the explanation given here: https://www.grammarly.com/blog/past-perfect/

...especially I like the example with the washable paint.