You could do it like that: Get your indicators with sequential=True:
myema = ta.ema(candles, period=5, sequential=True)
myema2 = ta.ema(candles, period=15, sequential=True)
and then you use their index like that:
myema[-1] > myema2[-1] and myema[-2] <= myema2[-2]
With sequentlial on: the index [-1] is the ema on the candle right now. [-2] is the one before and so on.
We check if the current myema is above myema2 and on the last candle was below or the same.