Point me in the right direction?

I am currently coming towards the end of a 12 week project for my Uni degree.

We have been charged with re-creating an old 14 century Abbey and its surroundings. I’m starting work on bringing in all our models into Unreal and building the environment. With the time we have left we need to quickly populate it with grass, trees, water etc. We downloaded Epic’s Open World Demo kit without realising you need a ridiculously expensive computer to run any of the textures, so unfortunately our machines crash after loading too much detail.

Can anyone point me in the direction of some less demanding assets to help us finish our project in time? Simple trees, grass and water will do! We would greatly appreciate the help as we are starting to panic!

This is free on marketplace:

However you need to make landscape materials.