I'm well into my IR, and thus far haven't learnt anything which has improved my flying skills (not an ego-trip, simply an observation). I took a current B744-rated friend up in my aircraft in solid IMC and without the AP he was in a right mess, found the workload overwhelming. He's a great pilot, but was simply out of touch with instrument flight at a rudimentary level. That doesn't make him a bad ATPL, just a fish out of water.
Like I said, it's what you make of it; 15hrs is nothing, but an experienced, capable, practiced IMC-rated pilot is more than capable of flying with superb accuracy. By the same token, an IMC holder who lives in VMC for 2 years then tries to fly a procedural ILS to minima is probably toast and an idiot for getting airborne in the first place.