In security terms, what is the difference between 15 and 24 word seed?
Therefore, which option is recommended? From a security point of view.
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Following the BIP39 standard, 15 word seeds are proving about 160 bits (20 bytes) of entropy, where 24 word seeds are providing around 254 bits (32 bytes) of entropy.
As long as you do everything to protect your word seed, 160 bits of entropy is plenty. In the past, people used 24 words to split it into two parts, but today they are better ways to split your seed, such as Shamir backup.
Little bit off topic, but I urge people to use hardware wallets, they are not that expensive and provide a huge increase in security over plain wallets - that is my security recommendation.