Can i get ban for saying ff 15?

Just saying it? Probably not.

Spamming it, saying it immediately after an ally dies, or in all char to indicate how bad your team is? Possibly, if you do it often enough that enough players think you're doing it as a substitute for calling them bad.

Personally I think one or two "ff15?" can be merited, as it's asking the rest of the team. :)

For saying it once? I doubt it. If you follow through with it and just give up and afk/purposely not trying to win until 15 minute mark? Most likely.

If you say "ff 15" once or twice, but continue to try to play the game, I have serious doubt anyone on your team would report you. At least I've seen "ff 15" / "ff 20" / "just ff plz" many, many times with the one who said it continues to help team fighting while triggering the surrender vote. No one on my team flame or threaten to report if they see that person still playing, still trying to win while acknowledging the game is a lost cause.

I don't care if you just saying it, minor annoyance, nothing more. However, if I see you push toward that goal by afk/feeding/not playing with team, i WILL report you.

no.

Not exactly, but more often than not, the people who go all "ff at 20" or the new one "at 15" more often than not rant their asses off and/or stop trying, which then it becomes a bannable offense.

I mean, Negative Attitude is bannable but i doubt anyone has been banned for it.

The official way to give up is with the surrender vote. Any other form of giving up, ex. opening mid, calls for ff, going afk, afk farming, ect can be punished.

That is not to say that it WILL be punished. Asking your team once, at 11 min, if they'd be willing to ff@15 is acceptable. You probably won't be reported for it, and even if you're reported for it, it won't count against you.

If you insult all the noobs that refuse to ff, say that you're going to afk farm krugs, have a dance party at baron, ect, then you'll make your way towards trouble.

mmm.... possibly?

That would incline "giving up" ig?

If you did that would be completely dumb ass hell though.