There are way too many permutations and combinations for anyone to do a half decent job.
with 1.5L mariott and 75k biz black europe or US is ruled out.
So you have to stick to SEA countries.
Singapore is what is possible, for 75k u can do 1 way krisflyer economy for 3, return you have to pay.
If you don't want to pay, then sri lanka through smartbuy u can do return trip for 3 for 75k points.
With 1.5L points, u can do 4 nights and 1 night free in singapore easily in base category room.
Sri lanka also u can do - but the issue is Galle, Kandy, Nuwara Eliya all u have to space out rooms and u wil miss out on 1 night free for 5th night and Mariott doesn't have good coverage in Sri Lanka.
Malayasia is also one option, only 1 way it would be free with 75k points in smartbuy.