We have Telekom Entertain over a 25 Mbps line, that works great. Telekom itself allows Entertain with 16 Mbps as well. It works, but it is really very little.
You always have about 10 Mbps for HD TV, and television always runs with priority. That means everything else is slowed down. If only 12 Mbps arrive out of these maximum 16 Mbps for you, it becomes tight for all other users. Multiple receivers at the same time are out of the question anyway, as is recording/watching TV in parallel.
So it depends on whether children/partner in the house also want to use the internet without disruptions. If not, it can work. It's definitely worth a try. If it doesn't work, you should be able to cancel the contract.
Is a line upgrade in sight? Entertain does offer many advantages compared to Sat, even if it is more expensive.
Just checked: According to the homepage, it is possible with 16 Mbps.