I'm a recent graduate who got tired of sitting at home. I went out and I got a teaching job (would be taking 2 subjects) at 15,000. I was asked to resume 2moro but whenever I think about the pay, I feel sad.

1) Should I accept it?
2) Should I go back and negotiate? (I made a mistake, I didn't really negotiate like that. He just told the price and I kept mute

I would advice that since you already agreed on 15k you should resume and work first for this term, its just barely 3months.
You can renegotiate before the beginning of next term.
Please take note at this time negotiations will strictly based on your productivity on the job so work hard to make yourself indispensable! They can't afford to let you go.
Finally, you can be more productive by suggesting a school management application where the school can generate revenue by selling result checking scratch cards to students.
Contact me for more details on this;
info@zeratech.tk

I guess u don't want to build a career in teaching, u just need the job to keep busy and sane while u wait for a better opportunity. if that's the case, accept the offer. U will be better off than staying idle at home. I hope u find a better offer soon.
Goodluck