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.

Note that on a 20amp duplex the ground pin is horizontal and on a 15amp duplex it is vertical. There are some 20amp units that accept either configuration.

And there are also some pieces of gear that use a 20a IEC inlet.

Point being that a 15amp plug will not fit into a 20a duplex or IEC receptacle.

The reason is that the committee in charge of such things wanted to make sure that consumers could not plug in an under rated power cord.

As far as what's a good 15amp duplex; there is a range from the classic Porter Port to the latest from Oyaide and Furutech. Take a look at VH Audio for an idea of what's out there.