Many thanks for your constructive feedback, which is much appreciated! It helped me a lot to prioritise my focus for improving the loading time.
I have removed the file reference for the images that create error in the source folder (images that I had used before but deleted later), thus the errors should be resolved now. I have deleted all "w;LsdException" from the code (I was not sure if I can do this but it seems that it is working). Loading time is still long I believe.
One thing I noted is that every time I export the project to a HTML5 document, it writes me this junk of apparently useless code into the index file. I have Googled a bit about this phenomenon and one suggestion was that this can happen when text is copied from a MS Word document into the project. I'll keep Googling about this...
The total size of all documents in the web folder (on the server) is 5,2 mb. I tried to reduce the size of all files as much as I could, but it is still a lot. I keep trying....
The png files have transparent background somewhere within the image which I need to retain. I have tried in photoshop to convert them to 8 bit pngs but the the transparency is only of acceptable quality when I save them as 24 bit pngs, otherwise I have sort of a white colour frame at the edge of the transparent background.
I have uploaded a screenshot of the file list that is in my web folder: