Been looking at that build lately.I was going to recommend 14cmmm as well. It's a good medium if you feel 12 is too small and 16 is too big. In an ITX build or even a mATX mini-tower then 14cmmm is probably your best option. 16 would look better in full ATX builds.
EDIT: This build from a Reddit post uses 16mm hardlines in the same case you have and I think it looks good. The ThermalTake Tower is probably large enough that the 16mm won't look oversized unlike in a SFF case such as the Meshlicious or Dan A4.
Also fixed cm to mm.
View attachment 489637