So it sounds like 50 mg daily for 90 days is the best case scenario for anything close to Iodine sufficiency. Either that and/or the 1.5 grams value (for total amount of Iodine in one's body) is way too low.
But yeah, certainly every body is different and so it is fair to expect no two people would get the same results from Iodine supplementation and reach iodine sufficiency at the same time.