1.5 delta isn't that bad on a 500. I only got my 400 down to 0.100. Adjust your Scale z-max all the way right to make it not look worse than it really is. Looks like you do have room for improvement in the back right corner. Right back tap it down, Left tap it up if the right doesn't level it out. Make small adjustments and re-mesh, one side at a time.
You only need to loosen the bolts for extrusions the motors attach to, each corner has two bolts. Shouldn't need to adjust the top. The commissioning guide gives a decent explanation on it.