Ok, it's only anecdotal, but if my little harmless gender-discriminatory way helps you convert more Indian Whatsapp groups then worth trying :). I've observed (in a completely non-scientific way of course) that in whichever groups that contains both men and women if a woman says "Hey all, let's move to Signal?", almost everyone will move quickly. If a man initiates that instead, you're going to get blank responses. So convince a woman in the groups ;)