RStudio: Stretched time series cross validation and using exponential smoothing models

I've been have trouble with a question for an assignment. I'm trying to apply an ETS model onto a stretch_tsibble in a time series cross validation. Running this either takes a long time to do or crashes my RStudio session. This is with one ETS model, my assignment requires three. I think there's a better solution to this and really need help with this.

My assignment involves using an ETS model on a training and test set then comparing it to a time series cross validation.