Is 700kb a good image size for a website?

I have an image with a dimension of 4000x2668 which I want to place in the background of the website front page. Is 700kb an okay size? or should I reduce it? I wan't people with 4k monitors to experience a high quality image but also make it fast enough for anyone in any device.

Also, I've heard about webp. I converted this image and it got bigger to 900kb. For me it doesn't make sense to use it. Should I?