question

You can create two labels in the source which count the output. Each label counts a different item type. You set the type of the current created or exiting item depending on the values of the two labels. If the sum of the labels reach 1500 released items you reset the values of the labels. You count by incrementing. This is a picklist option in the exit trigger.

You can build this method in ProcessFlow, too. A token waits for the creating event in a source. Then two labels are incremented depending on the label values and you assign the item type. If the sum of the two labels represent 1500 released items you reset the labels on the token.

Instead of waiting for the event you can insert a delay activity and then create the item with the depending type directly in the ProcessFlow. The following activities are the same as I described them above. At the end you let the token get to the first activity again.