First of all, no one has asked, "what benefits do you get?".
If you are getting medical, vision, dental, paid vacation, sick leave..etc then making $15 is not horrible (depending on where you live). With that being said, coming from a fellow engineer, you are getting underpaid...unless you have been with this company for less than 6 months (and the plan is to increase your status).
If this is not true then get as much from the the job as you can and begin searching for another one.
And just to let everyone know, salary isn't everything. I rejected a job that paid $15k more than the one I currently have...but I am doing much more interesting work, live in a place where I can ski, and this job gives me an advantage when I'm applying to graduate school...so salary isn't everything. It depends on what your career goals are.