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.