295/15=19.67, not 18.67
IQ and Chess Rating

Chess is not about IQ, but IQ can help.
Garry Kasparov has an IQ of 135. Not high as his chess skills

IQ tests include a number of subsets related to specific cognitive skills. An individual may punctuate high in several and average in a few others... those related to chess practice. Or the way around, very high in the cognitive skills used in chess but average or less than average in the others. So no, there's no correlation between IQ overall results and chess strength.
Besides, competitive chess practice demands a number of emotional skills that aren't measured in IQ tests. For instance, Ivanchuk's mastery made him a serious contender for the world title, but he lacked the emotional strength to do it.
Have you ever accomplished this so called iq test by yourself? It's absolute bs. I accomplished one a long time ago, my iq was quite high according to the test results. But I still can remember the test itself. And I am convinced, that this test indeed cannot check how smart you are. You can even train yourself for this type of tasks and you will get extremally high iq result. Also, I'm sure iq of famous people is actually fake, probably they have never ever completed any iq tests.