The calculator you are using to convert from lumens to candela is giving you “mcd” (millicandela) as it’s unit which is why you are off by a factor of 1000. If you want to convert a spotlight from lumens to candela you also have to double the outer cone angle for the correct value to enter as the “apex angle” (abstrahlwinkel in the german formula you used).
Calculating like that my lights seem to match up when switching from candela to lumens, so that part of the math appears to be fine(point light:1500 lumens -> 119 candela, spot light:1000 lumens 20°cone angle -> 2639cd).