... Speed 1.5 Gbps is the BUS limitation, not the SSD limitation.
ex for my computeur:

$ for i in`grep -l Gbps /sys/class/ata_link/*/sata_spd`; do echo Link "${i%/*}" Speed`cat $i`; cat "${i%/*}"/device/dev*/ata_device/dev*/id | perl -nE 's/([0-9a-f]{2})/print chr hex $1/gie' | echo "    " Device`strings` | cut -f 1-3 ; done ; echo ""

Link /sys/class/ata_link/link1 Speed 6.0 Gbps
     Device 30TRSSVAS 8MX4OACF0TOSHIBA HDWD120 )tk}iGsti AGc@ 4MBC
Link /sys/class/ata_link/link4 Speed 1.5 Gbps
     Device 220CD031077 RF03 hp DVD-RAM GH80N