Merge multiple ui images

Hello everyone. In my 2D app I create many gameObjects with UI image components(I work with new UI). These are simple colored circles. They are placed in different positions on screen. But when I play long enough, the count of these gameObjects becomes too high and it impacts performance. I though since these objects are just textures(i do not them to be animated or something, just simple textures that stay on the same place in the screen all the time), maybe there is a way to merge them into one gameObject with Image component that would hold all these circles in one texture? I tried to capture the camera view through RenderTexture ReadPixels method, but it captures the whole screen and all objects in it, while I need to merge only these circles and in a specific rectangle on the screen.