Yes, page speed depends on your page size as well as no. simultaneous users.
Each client has a bandwidth. So if your page size is high, the client will take some time to download all. Suggestion: Try to optimize images, css, js, everything you have
Each server has a limit on processor and ram. For every request, resources like this are used. Each server has an RPS - requests per second, it can handle. As soon as RSP increases, the server become busier and will be slow to send responses Suggestion: Do horizontal scaling