tire size question -- 195 vs 185

You may or may not have lost fuel economy, but the more likely explanation is that because you have installed tires with the wrong height ratio, you now have wheels with an overall larger circumference. Because of this, it affects the speed detected by the wheel speed sensors, which affects the odometer (reports fewer miles than actually travelled), and the speed displayed will be less accurate. This will have a flow-on effect on the fuel economy calculation. The car will travel further in reality than the sensors detect, so the under-reporting of distance gives you less economy, i.e., less MPG

The correct tire specification for the 195-width tire is 195/60/R15, so a 60% height to width ratio rather than the 65% you have fitted.