There’s an old habit (but a good one) on websites of stating the size of a document if it’s quite large. So you might see a link saying “(PDF, 3Mb)” after it. This was originally just a warning to visitors on slow connections, but nowadays it’s as much courtesy to those who have mobile data limits. If I can see a document is really large, and I’m on a mobile phone, I’ll bookmark it for later. If I don’t get that warning, and it’s still downloading after 5-10 seconds, I normally abort the download …and may not bookmark it for later. So it’s still good practice.
What would you consider to be a large document? 1Mb? 5Mb? The latter would, after all, take several seconds to download on mobile 3G connections.
What would you say if you discovered your home page was actually that large? Because on many sites, that’s exactly what it is.
Check out your site at an online speed test tool such as GTMetrix, which I’ve mentioned here before. Pay attention to the “Page Details” panel (above). If you see page load times of more than about 5 seconds, of course you should be alarmed. But check out the page size too. Do you really need to be throwing more than a megabyte of data at your visitors?
Your website designer, perhaps in conjunction with the website hosts, should be able to resolve such problems. In my experience, very few of them seem to care, favouring flashiness over efficiency. You’ll have to push them. Be firm.