I'm sorry say it, but in my opinion at least, jawfish are not great beginner fish. If you totally research them & follow the best advice out there, it might be ok - but there's a lot of info out there from people who had one for less than a year.
I don't know how deep your tank is, but after you put in the correct & deep enough substrate, it might be rather shallow for a fish whose startle response is to shoot straight up really fast -- basically out of your tank. It doesn't have to be another fish, it can be someone walking by the tank, for instance.
My vote is 15g is too small for a jawfish.
Smaller blennies, 1 firefish, royal gramma, pink skunks, oscellaris, highfin gobies, clown gobies are just some of the nice alternatives you have.