Every web page is actually a collection of data - text Images, graphics video etc
It is normal for a browser to download and Cache this data locally (on the SSD in your case), in order to display the page this data is retained for a short period as having the data for headers and the like available locally speeds up the loading of other pages from the same site.
When the browser is sure that the data is no longer needed the cache data is deleted.
Some sites do work differently when dealing with the large amount of data involved with playing video - data is streamed, continuously fed directly from the source (Web) to the screen but even here ther is some small amount of caching to enable smooth playback
This happens with all drive types, so is nothing to be concerned about
The Browser is also known to write it's own required data to the local drive for Cache purposes and this is also deleted when no longer required - the 1.5 GB per hour written can actually amount to a small amount of data at any one time it could be that the amount on the disk at any one time may be measured in Megabytes or even Kilobytes as the data is deleted often during the same hour quoted