How can I speed up my website?
If you go to the Edit Slider → under Slider Settings → under Slides → Image Load, then you can find a lazy loading option. With this option you can make your slider to only load one slide (or a few more), and this way even if you have lots of slides, your slider still can be fast.
In your slider you should use images which are having the same ratio as your slider, and they should be as wide, as your slider's maximum width on your website. Almost every people, if not all of them will look at your website on a 1920px, or smaller width screen, so if your slider has 100% width, your images should have 1920px width to have the best quality. Pay attention for the image file format too, jpg images are way smaller, then png and gif images. But an image with optimized size can still have a big filesize, if the quality is too high. At a certain point, people's eyes can't see the difference in the higher and lower quality, so you could try to save down your images with lower quality, and as long as you see it the same, you could lower it's quality. You could do this if you have, with Photoshop, or if you don't, then with GIMP, which is free.
You could also optimize your website's size by picking device specific images to load smaller images on tablets and phones. Or make other two sliders with the smaller images and you could also load less slides in them, then load those sliders for tablets and phones. You can do it like this on Joomla and like this on WordPress.
Usually people doesn't know, what is loading for how long in their websites, so the best thing you can do is to google "website speed test", and check the files' loading speed. This will help you to find out, if you are using too big images in some places, which you could replace, and if something else is loading for too long. At the first line you will see the Time to First Byte, which means the amount of time until the first byte is received from the server, and that can indicate, if your server is slow, and you might want to consider moving to another, you could also try to contact and ask them about it, but usually they will just say, that everything is fine at their end. For the files, the connection time can be longer if there are too many processes and connections at the same time, and they have to wait in line. You shouldn't use many extensions, modules together, because even if they are small in filesize, the loading time will increase even more. And just because you have a small website, as in byte size, loading many files will take way more time, then to load a same size website with much less files. You should have your extensions updated, for example this way you would only need to use one jQuery, the code of Joomla, php is getting optimized in time, and the extensions can use these new, faster codes too.
If you are not using Google fonts, then remove them from loading like this.
But if your website's speed is really slow (~ more than 30 sec), then probably there is a problem with some code, and you should go to the Extensions → Plugin Manager → filter out the system type plugins, and disable them one-by-one to see, which one is causing it.