I now have the 15 hours instruction in my log book but no actual qualification. My question is, do I actually need the IR(R) qualification in order to build IFR hours towards the CB-IR?
If you mean "Can the 15 hours be
credited towards the 40 hours required by the CB-IR, despite me not having taken the test?" then the answer is yes. If the question was "Can I
build more hours under IFR towards that 40 without an instructor?" then the answer, as Genghis says, is no. Any such further credit must be using a rating that permits flight under IFR.