Are the reports that led to the ban cleared from tribunal after the ban? Or are they still counted toward a next offense?

ie: Player got 15 reports and got banned. After ban period, goes back to game, gets 1 report, will he be sent to tribunal with 16 reports?

They are cleared but the punishments add up, although there are people who disagree with this.

The reports stay on the character but they arent what is shown in the tribunal. If that makes sense that is.

One thing that may (or may not) be happening is that inbetween the time of the games that are in your case in the tribunal and the time you are banned, any reports you get are not cleared. Conjecture based on people posting about being banned twice despite changing their behaviour after the first ban.

Only the reports in that case are cleared (up to 12 I think).