I wonder whether this is something that happened all at once or gradually over time? Also, do you notice it in specific webpages with a lot of graphical content?
Even though you have a full-sized laptop, it contains a processor that was originally designed for use in small budget netbooks and tablets. Up until just a couple of years ago, they could handle everything that a casual user could throw at them. Web browsing was nothing. However, CPU-intensive HTML5 content has been spreading like wildfire, and it slows some of those processors to a crawl. My Asus T100 2in1 used to be fine on any website, but now even things that used to be simple like Google Maps or CNN are absolutely frustrating.
One imperfect suggestion that might help a little IF this is the main problem is to change the user agent string of your browser. *Some* (not all) websites optimize for multiple form factors. If you use something like https://chrome.google.com/webstore/detail/user-agent-switcher-for-c/djflhoibgkdhkhhcedjiklpkjnoahfmg/ for Chrome or https://addons.mozilla.org/en-US/firefox/addon/user-agent-switcher/ for Firefox and change your user agent to something like Android or iPad, you *may* end up getting a version of the website that is more optimized for a tablet processor. That will definitely have some downsides, but it might also render quite a bit faster for you.
If this happened suddenly or occurs in all websites, my suggestion won't help you. It's more likely that there is something actually wrong.