I am guessing it won't be easily fixed. The reason they probably have the high speed turning, particularly with unprotected left turns, is the difficulty in finding a big gap in oncoming traffic that would be needed with a slower turn.
Furthermore, even with a bigger gap into which you are turning, that gap can close quickly as you turn, if an oncoming vehicle in the lane you are turning into, is moving faster than FSD estimates. So when you have a chance to turn, rather than wait until you don't, the car races to complete the turn in order to avoid the oncoming car. For Tesla to slow down the turn, they would have to wait for a bigger gap or be better at estimating the speed of the other car coming at you, while you are turning.