I'm not familiar with the 115, but on my 108 there was a third bolt. One at the top, one lower right (looking in from grille)and the third just left of the pump. All were 13mm and that last one was tough to get at.
Side note: once all three were loosened, the pump still would not budge. Determined that the wrong belts had been put on by prior owner or PO's mechanic. I could not put any slack into the belts as the pump was bottomed out already. Ended up having to remove the fan and clutch to remove belts. Proper belts are now installed.
Also, if the belts are too tight, the pump can be damaged. Learned that one the hard way.
73 280 SEL 4.5