In order to terminate a futures klines stream, we need to pass the full ws endpoint URL, what is easy for spot, but not for futures because there is no getFStreamUrl implemented, which could be as following:

getFStreamUrl() {
        if (this.Options.test) return this.fStreamSingleTest;
        return this.fStreamSingle;
    }

This ways I'll could disconnect from a future stream using (similar the way I do for spot):

const streamUrl = this.binance.getFStreamUrl() + "btcusdt@kline_15m";
this.binance.futuresTerminate(streamUrl);