Suppose, I buy XRP and set limit of 15% fluctuation. The coin should immediately be converted into Monero if this happens. Is there any exchange which offers this function ?
How do you define a 15% fluctuation? It depends on the timeframe you're looking at. I'm guessing you want to set some kind of alert or trigger if the price jumps around that much. The more advanced trading platforms let you set stop-losses and take-profit orders and stuff like that, so when the price hits whatever target you picked, it'll automatically sell or buy or whatever. Thats probably the easiest way to automate what you're talking about and
However, if you need something more custom, you'd have to set up your own trading bot. It uses the exchange's API to check the prices and execute trades programmatically based on the rules you set up. So yeah easy way is use the platforms built-in orders. If you want full control, make your own bot. Just depends how sophisticated you want to get with it.