Client VPN slowness

It may due to the internet connectivity speed and latency between your Windows PC and the Web EC2 if there is large among of data to be transferred in order to be load up a page. You can consider trying with another internet connection.

There is also another option that you can consider is running AWS workspaces (https://aws.amazon.com/workspaces/) such that your desktop client is close enough to the Web EC2 and you just send the screen output instead of the page content to your Windows client.

The number of seconds are unlikely caused by latency, even with very sub-optimal routing. This looks more like a timeout issue on some of the resources. I recommend that you look into the developer tools of your browser. Many have support for recording the network traffic. Check what is happening during the 5-10 seconds and look at the destination URLs. Maybe your web application is loading fonts or JavaScript from other web pages. Check the reachability of that URLs with and without ClientVPN. I guess you will find an indication here to decide on the next steps.