Images getting loaded really slow on github pages

I created HTML/CSS/JavaScript landing page, with a lot of photos (around 300). About 290 photos are displayed with lightgalleryjs for a modal carousel and I added loading="lazy" attribute to each image.


When I view the website on browser via local server it's fine and loads fast but when I upload it to GitHub pages it takes about 10 - 15 seconds to load the images, a background video (without loading lazy) at the header also takes a lot of time to load (it wasn't the case with GitHub pages before I imported the photos for lightgalleryjs).


How do I solve the slow loading of images?