The circuits are virtually identical. The circuit board layouts have subtle differences.
The best I can tell, the 160 was c1990 and the 115 was c1991. Around that time, Peavey transitioned from hand drafted schematics and mechanical prints, and hand taped circuit board layouts to CAD. It would seem that they needed to redo the entire design for entry into the new system and to work with the new automated circuit board manufacturing equipment, so that new version was dubbed the 115. The 160 was the end of an era so to speak.