Best way to convert particles and sprites in a single sprite at runTime

I am developing a 2D game where I need to keep all the blood, debris and stuff into the stage until the end of game, just keeping all that sprite/partciles until the end would not be possible. My idea: in a fixed period of time I convert all this sprites and particle system into a a single 2048*2048 sprite.

I was thinking about using a secondary camera culling into a specific layer with renderTexture to do so, the problem: I can find a way to convert the RenderTexture into a sprite.

I am not sure if this is the best method to doing that, if isn't, what is my best option?

The game is target for Mobile and PS vita, so i need it as light as possible.

Thanks a million! Hey guys I still having the same problem. No one could give me a hand here? do you think the situation is poorly explained? I was expecting more answers here...