Someone on macrumors has seen an SSD model and its 1.5 also! some are saying it maybe to help achieve the 7hr battery life, time will tell. Something isn't right about it all.
If you are using the 9400M, you will certainly get better battery life. However, since you said you're getting the base model 15in MacBook Pro, I hope you're aware of the fact that it does not come with a 9600M GT graphics card?
If you get the higher MacBook Pro model, it seems you can't switch between the 9400M and the 9600M GT in Windows according to this article.