No one here can answer that question. We have no idea how many BTU's your burner is. We don't know how vigorous you boil your wort. The good news is that you can answer that question yourself. Put five gallons of water in your new keggle and bring it up to a boil. Once boiling commences, start a timer. After 60 minutes, turn off the burner, let the water cool and measure the volume remaining. Subract the volume remaining from your 5 gallon starting volume and that is your one hour boil off rate.
It's important to measure the remaining volume cold, since your starting volume is also cold. You could measure it hot, but you have to take the 4% shrinkage amount into account if you measure your final volume hot.