It took me two prints to get this right, but the second try came out absolutely gorgeous.
The first version was printed laying flat with the base on the print bed (original leaning position). Additionally I used supports, even between the pillars, because I did not trust my printer regarding the archs. The result was very poor and I destroyed a couple of pillars trying to remove the support between the pillars.
The second version was sliced in ideamaker. I used the "lay flat"-option of ideamaker and picked an element of the top surface of the tower. This resulted in an upside down standing tower, which I simply had to rotate by 180°. This way I had a perfectly straight tower, without any further need to adjust. The only thing that was left to do was placing manual support underneath the base plate and the bells in the top of the tower - no further supports needed.
I printed this in 200mm height. Thank you very much for this nice model. My son will use it in school to talk about the leaning tower.