If the adhesive is not cement based you could try sprinkling water to the wall to ease the scrapping process.
How to remove old tile adhesive from wall.
Give a few taps until the tile adhesive becomes loose enough to fall off or be scraped off with the end of the chisel.
Irrespective of the adhesive formula you have to cover the floor with old cloths as to protect it from the residues which will fall off the wall.
How to remove ceramic tile glue from a wall.
Wait several minutes and use a large scrapper to remove the mastic.
Chisel large chunks of tile adhesive off the walls.
Apply an adhesive removing paste to the wall.
Place the chisel at the edge of the piece of adhesive holding it at about a 15 degree angle.
Usually when you chisel the tiles off most of the thin set mortar will be removed with it.
Apply some water to a small section of the adhesive.
You will then have to pry off the leftover residue.
Since not all will come off there will be an uneven layer of adhesive left behind.
Use your hammer to gently tap at the end of the chisel to pry off the adhesive.