Carrying a drop loop holster made for a 2 inch duty belt on a standard trouser belt is rife with problems. The holster is going to shift around and depending on how new or used the holster is, the gun may not draw as smoothly as you would like as the holster will shift during the draw. There is a great picture in Jordan's book, "No Second Place Winner," where he is drawing his Model 19 from a Jordan holster and it is pulling the holster and gunbelt with it. Jordan advocated looping both the trouser belt and the gunbelt through holster loop to prevent the holster from shifting.
A holster with 1 3/4 inch slots on a 1 1/2 belt should not be a problem, assuming the belt is stout enough to carry the weight of the gun. Don't use a cheap belt; a trouser belt used to carry a handgun should be as strong as a duty belt since it must carry the same weight.