How to calculate server speed ?
You can use this tool which is available in this URL: https://www.uptrends.com/tools/website-speed-test
Using command prompt you can ping your domain or Server's IP address. You will get the server's latency in ms.
Above all: You need to optimize the website by contacting your website developer. Please find some of the useful links below.
https://www.uptrends.com/tools/website-speed-test (Select New Delhi, This is correct way of testing)
If you think, You have optimized the website correctly still want to improve the page speed, Then consider upgrading for Premium hosting or VPS servers.
We have written in great detail here, Please read this link.
Use this chrome plugin to find out the "real loading time" of the website. https://chrome.google.com/webstore/detail/page-load-time/fploionmjgeclbkemipmkogoaohcdbig?hl=en
You have to install this plugin.