15 words Seed possible?

I want to restore my 24 seed phrase word list that I from my nano x but it says invalid. Now strangely if I type in the first 15 words in a Wallet like MM or mycelium, it says that its valid and gives me an account with no btc nor eth balance. How likely is this? Is there a problem with the derivation so the wallet doesnt connect to the addresses with balances on, or is this just a pure coincidence. In that case what are my options of recovery?

thx

15 words Seed possible?