I think you should be fine, as long as you keep some things in mind.
- First of all... what is full-size? 480p? 720p? 1080p? Construct will scale the images up or down regardless of resolution, but the size you choose decides how big the image will be. It depends on what your main target resolution will be.
- How many layouts do you plan to use? Because one layout = one more image.
- Do NOT move these big background images. This costs a surprising amount of power. Move the viewport instead.
I can only guess but if you go for 720p png images you should be able to go for ~1mb per layout. Also depends on how many colors you use (how good it compresses) or you could instead use jpg or gif (lower quality, lower size). Or you could load the images from a server. (Requires internet connection though)