In case you're interested, here's the train times:
🇩🇪 Berlin 08:17 - 13:19 Koln 🇩🇪
🇩🇪 Koln 13:42 - 15:35 Brussels 🇧🇪
🇧🇪 Brussels 17:56 - 19:00 London (St Pancras) 🇬🇧
🇬🇧 London (Kings X) 20:03 - 22:21 Leeds 🇬🇧
Not home yet but my main takeaway is that although 15 hours (!) sounds awful, it's been a breeze!