Poor performance relative to other Sandisk Ultra II SSDs

I am helping to improve system performance on a HP14-an019 which has a Sandisk Ultra II 256gb installed.  The SSD was put in by the high street retailer (not HP), and obviously something has not gone to plan!!  The SSDDashboard reports all good, and Firmware is X41200RL.  Processor is AMD A6-7310 and 12GB of RAM,.

Just looking for advice or comments in the SSD before I take an image and then reinstall windows on the (cleaned) drive, and failing that working, contacting retailer to look at replacement (which will mean quite a while with no laptop).

does your MB have a SATA III controller and is the drive connected to that controller?