Um, yea, that is huge!
I can’t say I blame your computer for not responding.
If there are a bunch of components that you downloaded but decided not to use for some reason, you can try purging the model by going to Window menu >Model Info>Statistics>Purge Unused.
I think there may be plugins for reducing file size, I’m not really familiar with very many plugins.
But my strongest advice is for you to try to use only low-poly components from the Warehouse. I know there are some beautiful landscaping items available, but most of them are far too big to be practical in a “big garden.” Many of the simple, smaller components will do the job, if you choose carefully.