After 4 years, the site began to slow down on mobile. How to figure it out?

Question

Web development

Immediately disclaimer, I'm not a development professional, this is not my specialty.

Made a website 4-5 years ago. It's self-written in jQuery. Adaptive. At that time (2016) it was tested and worked fine in browsers, on a desktop and on a smartphone, everything was fine and fast.

But now I discovered that the site slows down on smartphones, and not in terms of traffic, but it looks like JS. At what point it started, I don’t know (I rarely look myself). From the moment of creation and debugging, I didn’t do anything with the site, didn’t change any code, even the content of the main page remained the same. Of the changes: except that I installed an SSL certificate. Questions:

1. With what brakes which were not can be connected? And the desktop version works as well as before.

2. How to profile the site on a smartphone (on a desktop, I know how) in order to understand the problem?

(If you are not too lazy, take a look at fasadel.com, maybe for the pros the problem is on the surface.)

Answer 1

developer tools, performance tab.

Answer 2

You have images with a width of 1920px for the mobile version, which is not necessary. For example, this is - https://fasadel.com/img/54447.jpg
For mobile devices, graphics can be processed separately.