Why is the webview application running so slowly?

Question

Java

Greetings. Created a simple android studio application that displays my website. The start page is made sewn, i.e. All site files are located locally. In principle, everything works, but terribly slowly. For example, if you click on a link from the main one, then the main one hangs and costs 20-30 seconds, and then it just starts loading what is on the link. I've tried everything, I don't know what to do. Then I thought that I need to remove something or change some parts of the code in some places in order to somehow speed up the work. Here is the source of MainActivity.java

PS Yes, the code is so-so. Do not judge strictly, I'm a beginner.