1.5 GB will make a small difference at least, but may not be worth the cost. Open Console in Applications>Utilities, are any messages repeating as you work? Then open Activity Monitor, click on the System Memory tab, report the # of Page Outs.
One free thing that may speed it a bit, I think you should get Applejack...
http://www.macupdate.com/info.php/id/15667/applejack
After installing, reboot holding down CMD+s, (+s), then when the DOS like prompt shows, type in...
applejack AUTO
Then let it do all 6 of it's things.
At least it'll eliminate some questions if it doesn't fix it.
The 6 things it does are...
Correct any Disk problems.
Repair Permissions.
Clear out Cache Files.
Repair/check several plist files.
Dump the VM files for a fresh start.
Trash old Log files.
First reboot will be slower, sometimes 2 or 3 restarts will be required for full benefit... my guess is files relying upon other files relying upon other files! :-)
Disconnect the USB cable from any Uninterruptible Power Supply so the system doesn't shut down in the middle of the process.