You needs to do a SMC RESET procedure on the MBP after the installation. It might help reset the AHCI driver to the new SSD disk to get the 3.0Gbps negotiated link. It might work depending on the revision of the MCP79 chip that the MBP uses. I have the same model and researched all the problems with it.
If the SMC reset did NOT work, you are stuck with 1.5GB but be happy that the disk actually works because others are getting ramdom hands/slowdown and after a few weeks the SSD becomes DEAD (would not boot anymore).
On the OCZ models, they did a firmware tweak to FORCE the link to be SATA2 to get the 3GB speed, but this will make the CD driver not workable in some cases. The issue here was the AHCI specs were not implemented fully by Nvidia and there are power issues when the drive is operating. On many cases, a large read will cause the beachball wait effect since the drivers will be reset by the hardware several times in an effort to recover the operating link. It will reboot if the condition gets worse. From what I hear , OCZ nailed the problem at the expense of CD driver operation which is acceptable to the user. Apple never wanted to do this for fear of legal repercussions they might endure. So OCZ is the only way to go for this MBP model becuase other drives with SF 2281 controllers are having serious problems. There are people with Rev B logic board that did NOT have such a problem. Unless, you had your board replaced recently, you are likely stuck to the Rev A board which had this weakness.