The G01S pads are slightly wider, and slightly shorter, than the B01S which you replaced them with. If you compare backing plates carefully you will see the difference. I know this because I thought they were all the same but a genuine Shimano bleed block wouldn't fit in a BR-M395 caliper that has B01S as the specified pad. You may need a digital caliper to measure the difference.
Thus you can stick the smaller B01S into a G01S hole, but not the other way around... A G01S will not fit in an Acera BR-M395 caliper (or a BR-M315, BR-M355, BR-M396, or Alivio BR-M445, or others that have th B01S as OE). I wouldn't use the B01S pad in your application because it'll be wiggly in your M615 brakes - The loads from braking are transferred to the beefy sides of your caliper, the through the caliper to the frame. Wiggly pads will "wear out" your alloy caliper, making the hole bigger, and applying a torque to the split-pin that holds the pads into the caliper.
It probably isn't dangerous our anything, at least not over the life of one set of pads, but it will chew up your calipers some, which is more expensive than buying the right pads.