Only possible if the colluding miners have almost all the hashing power to themselves (to mine 6 consecutive blocks faster than everybody else). If that's the case then those miners can do anything they want anyway, including double-spending money[1].
Furthermore if they really only wanted to slow down BCC and nothing else it still wouldn't be very efficient. They'd just postpone the scaling for the next 6 blocks and then the rule would kick in again. So they'd have to keep make sure that they're always just at the limit of 6 blocks per 12 hours... but at this point you're actually mining block and contributing to the ecosystem, so there's no problem.
Furthermore if they really only wanted to slow down BCC and nothing else it still wouldn't be very efficient. They'd just postpone the scaling for the next 6 blocks and then the rule would kick in again. So they'd have to keep make sure that they're always just at the limit of 6 blocks per 12 hours... but at this point you're actually mining block and contributing to the ecosystem, so there's no problem.
[1] https://bitcoin.org/en/glossary/51-percent-attack