help for optimizing my scene

hello guys i have problem if someone could help plz - this question related to optimization issue -
i did watch a lot off YT videos on how creating landscape master material with blending layers - and they said - to not pain many (or more than 4) layers in same component off the landscape ----- now i did some tests and i found out that every texture i use in the material will be loaded in memory (u can see it from statistics * texture stats) — is that a bad thing ? because i have like 10 layers for the landscape - and all textures are loaded in full dimension 4k (bc the player is close to landscape i guess) and the textures (landscape only 4k res) takes like 500mb of ram (is that the pc ram or gpu ram?)

sorry for longe post

and is there any good source on how the render really works ?