Have you had a chance to test this against 3.2.9 and/or 4.0.5 as well? There has been quite a bit of fine-tuning in that space lately... You might nevertheless see the same effect but it'd be helpful to verify against those most recent releases.
This looks like a consequence of #15981 then, which we addressed as of 4.0.1. Since we have a dependency on JDK 6 and even a specific JDK update level there, we can't easily backport this to the 3.2.x line, I'm afraid. So the generally improved behavior is a 4.x only characteristic.
That said, we did introduce a "spring.beaninfo.ignore" property in 4.0.1 and 3.2.7 - see #13653. Setting that to "true" (as a system property or in a spring.properties file) will suppress the entire Introspector BeanInfo handling, which might optimize the GC load in your scenario. This is the only option in that problem space that's available in 3.2.x line as well.