Unity memory thirst

I have an app with 3 scenes. It's a 2D Game. My texture memory never goes further than 32MB. It's usually around 25MB. In my second scene, the one with the highest cost, I have around 130MB. If I put the app in the background, open other apps that take lots of memory, it goes down to about 30MB. Then I can just reopen the app and just keep playing as usual. The memory goes up back to around 130MB in 5-10minutes whenever I change scenes.

Why does unity reserve so much memory without returning it to the OS? I mean, if you have an app that can function with 30MB, Why request more memory when you already have 50MB? On older devices the app gets killed because the app requests too much memory even though it does NOT need it.

Is there a workaround that'll leave me with enough memory on older devices?