I can not rate OKX because it is no more available in my country, but it is consumes low data than other exchanges when I was using it.
OP, may we know your Top 3 out of 15?
No exchanges like Bybit for now for the best Android app. Others are not comparable with it.
Then followed by Gate.io
I am not a fan of centralized exchanges that can spy more with closed source apps, but I love what Peach Bitcoin app is doing for non-kyc bitcoin to cash trading.
Vexl app is another solid alternative app but you need to connect it with phone number to use exchange.
I can not trade future on peach bitcoin wallet. My trading experience is better on those centralized exchanges. Bit we should remember not our keys not our coins.