It will be hard to distinguish between 1.5 Gb/s and 3 Gb/s by measuring the hard drive speed. 1.5 Gb/s can do top of 150 MB/s so you may see 100 MB/s on it, but that is also around the speed of ordinary SATA disk drives, so how can your tell?
In any case, as already mentioned, you won't see the 3Gb/s, but if you still want to know what transfer mode the drive is using, CrystalDiskInfo seems to be able to distinguish the mode. I have a 6 GB/s SSD and hard drives on SATA 6Gb/s ports and 3GB/s hard drives on 3Gb/s ports.. CrystalDiskInfo shows the transfer mode for the 6GB/s drives as SATA/600 and the 3 Gb/s drives as SATA/300. Crystal Dew World