An SSD for your catalog will help. IMO, a new graphics card for a machine of this age would be a waste of money.
If I was able to find a video card - there's a couple of places that sell used cards (not e-bay) - what would I need to be looking at to make any difference for LR and PS CC 2015?
Would the the slow updating of the image in Develop have anything to do with the video card?
Have a look at this document, which answers a lot of the questions associated with GPU Adobe Photoshop Lightroom Help | Lightroom Graphics Processor Acceleration (GPU) Troubleshooting & FAQ Personally, I think you'd be best saving your money for a new machine rather than buying a graphics card that will more than likely have minimal positive impact.