Large terrain workflow(s) question

Hi all. I'm hoping a seasoned vet can shed some light

I'm deving a mobile rpg and I'm concerned with keeping performance as fast as possible. My world can essentially be broken down into 4 500x500 terrain objects - They have NO deformation, I am only using terrain for it's texture painting functionality (painting roads, trails, etc).

I've found that Micro Splat (free version of Mega Splat) will atlas 16 textures into a single draw call, which sounds great for my purpose as I was concerned with how Unity adds additional draw calls for textures added after using the initial 4 within the terrain object

I'm wondering if there is a better, performance oriented approach to achieving the same thing, or if I'm worried about something that I shouldn't be worrying about... IE, instead of using a terrain mesh, import a single quad and paint on that, or is that just over optimizing, etc...

Thanks

 

so is the terrain completely flat surface? surely mesh would be much better then in every way (file size, memory, drawcalls..)

 

Yea, as it stands right now the terrain is completely flat. Even if I were to create hills or elevated sections, since this is a mobile game, I could surely create the landscape with geo and have it be much lighter regarding very counts, etc. The main concern is dealing with painting these large areas with multiple textures while maintaining performance. I'm curious what others have found successful in the past