There are many reasons why you may not be getting as much speed as you think you should. A few things you can do you make sure its not on your end. Also mentioned above its up to 1.5Mbs not exactely 1.5Mbs. On average you should see around 1.1-1.3 depending on area. If you are going through a wireless or a router that can also reduce your speeds. Mostly if someone else is also on the network at the same time. Some sites have caps on the download speeds you will get. No matter how good a connection you have if a site caps it at 500kbs then that is what you will get.
First do the speakeasy test. It can give you a ball park on your speeds though you should do more then one test and test different locations (sometimes a test site can be giving off very low readings).
If you are not using norton you should make sure to remove it completely. Either with NRT or new remove option it now gives.
Make sure you do not have any background programs taking your bandwidth. If you desire you can boot in safe mode with networking and test your speeds that way.
Next step would be to call your cable provider but there will probably be a service fee. Most slow speeds are the result of customer equipment or an improper install (if on cable unsure on dsl).