Over 12 billion doses have been administered. Using your claim (100 times worse than 1/15000) we should expect to see 800 million cases of transient heart issues. It seems unlikely that such a number would go unnoticed
Per OP, we should see heart-related issues for 1 out of 15'000 vaccines administered and hence to 7500 people, which is already 100x more than what it should be.
Comes out to be +0.013% increase.
However, [1] says 30M adults in the US were diagnosed with heart-related issues in 2018: these could be mild to severe issues. This is out of ~200M adult population of the US [2], so a rate of 15%. Note that these are the number of patients diagnosed - many more could potentially be undiagnosed, more so in developing and under-developed countries.
225M people have been administed Covid vaccines in the US. Per above statistic, at least 33.75M should've heart-related issues at some point in their lives under normal circumstances.
So, now, as per OP's claim and from what I understand, we should see +0.013% people being affected by heart-related issues at some point in their lives that can be attributed to vaccines, which comes out to be ~30'000 more people.
My own research tells me the months long cardiac issues I got when getting COVID happen 100 times (or more) frequently.