Is it okay to plug a 115v (15 amp) A.C. window unit into a 220 circuit plug??

 

No. It will burn the compressor and fan motors out right a way.

Use a stepdown transformer or if you are in the US or some country that uses the standard split 240 VAC (120 - 0 - 120 ) system just use one half of the circuit.

 

Is it okay to plug a 115v (15 amp) A.C. window unit into a 220 circuit plug??

Absolutely not! The plug will prevent you from doing that; unless you do something stupid.

A member posted about doing this inadvertently, due to a wiring problem, and it blew the fuse and MOV.

 

If in N.A. and it is a dedicated socket, you may be able to swing one conductor over to a neutral in the panel and change the breaker and outlet, the conductor assigned the neutral should be marked with white electrical tape at the junctions.
Max.