If it's a 2048 word list, then 6 words is 2048^6 = 2^66 possible combinations. Not impossible. That is just over 1 year at 2 trillion keys per second.
Now, give us example of wallet which uses 6 words as seed mnemonic since AFAIK most wallet uses either 12, 18 or 24 words which means time required is far longer.
An earlier post states that 17 of the 24 words were revealed, so only 6 words need to be brute forced.
If the
positions of the revealed words are known then you could recover up to 187 bits of the 256 bit key, and instead you would brute force the unknown bits.