System resources - Low Memory!

I've just moved all my projects and relative folders on an external SD card so to free up internal memory.
When checking it it says drive size is 14.4 Gb and free space is 6.0 Gb.
When I load the project which resides in the SD card, which is 1.3 Gb, I get the "System resources - Low Memory!" warning message.

What am I missing here?

Memory is not storage. Memory is ram, it’s what holds all your samples in the currently active project. The internal disk stores all your content, ready to be loaded into memory when needed. Your project is too big , it won’t fit in the available memory

Ok, that makes sense.
Thank you