What file size do videos in websites start at?

I have barely worked in Premiere pro or with video in any way. I have put together a 15-second clip of footage in premier and have exported it and it is about 20mb. The video is for a website I am working on, it will be the hero image on the homepage which will loop through, I am sure you have seen this style of video in websites lately.  Current export setting are (which i have set after researching 'how to export video for Youtube' forums on Adobe support and around the web): H.264, Youtube 480p SD wide, unchecked audio, target bitrate 10, maximum bitrate 12.

My questions are: What would the standard file size of a video of this style be? Is 20mb massive, or is this a normal size file of a 15 second? If I am able to reduce it significantly what settings do I need to change? What size file do people normally upload to youtube? What is a standard file size of a video in the homepage of a website?

Thanks guys. Trying to learn the very basics of video so happy to hear anything that might seem obvious to you, as I have probably missed alot!