casperes1996 is correct. The free space on your SSD isn't a factor.
How much RAM is in there? 8GB is your maximum. Even with 8GB, the MBP may be doing a lot of "paging" (using the SSD as RAM) depending on what you're doing…and the SATA bus speeds on those old MBPs are a modest 3 Gb/s which will make the paging even slower.
Stay away from Google Chrome and, probably, any other Chrome-based browser. I have an old MacBook and it's such a hog that normal browsing makes the fans kick off.