Upgrade Receptacle on 15A breaker

Sound, No not necessarily. 12 guage is code for 20A. This topic is covered in other threads, but I suggest you call a licensed electrician.

Use any kind of outlet you fancy. The current drawn depends on your equipment, not the outlet, and probably doesn't exceed 3 or 4 amps except for a surge at turnon. If you short out the outlet the 15 amp breaker (or fuse) will open. In other words, an outlet rated for 20 amps will not increase the current drawn through the 14 gage wire from your service entrance.

shouldn't a line with a 15A breaker go no higher than a 15A receptacle?

No, it should go no lower than a 15A receptacle.