It won’t go through IFTTT. Just Alexa. But, yes, there may be some additional lag, you will just have to try and see
Read the FAQ, it has a link to the code that you will need for the virtual device. The FAQ is for doing something the other way around, using a SmartThings event as a trigger for an Alexa routine. You’re trying to use an Alexa event as a trigger for a smartthings automation. But you’ll use the same kind of virtual device as the go-between. 