SL-L (StopLoss - Limit) order becomes and behaves like Limit order once the Trigger Price is crossed. So once the trigger price is crossed, this order will not get executed till market comes back to limit price. There is always a chance market breaks the trigger price violently and hence the limit order may not get executed immediately especially so if trigger price and limit price are same or very close by.
If one want the exit the market as soon as trigger price is crossed, then one has to use SL-M (StopLoss - Market) order which will get executed immediately.
Check out this link on z-connect.