I know of two coins which are Atom and Dot. You can stake them to earn. The APY for atom is 18% while the APY for dot is 15%. For the dot, the minimum amount that you can stake is 270 DOT. You can stake this two coins on noncustodial wallet that support their staking. There are other coins but which I can not advise anyone to go for.
crypto exchanges upto 15 % - but are they safe to put money there ? like nexo , kucoin ?
Not your key not your coin.
I understand op didn't specify if he wanted apy on usd or whatever but I wouldn't consider staking alts to be a safe investment. One of my friend invested in $DOT during last bull run and put into staking and now his staking amount although has increased but dollar value is marvelously lower from what he invested.