1.3.2 was released in May 15, 2019, whereas 1.5 was released two weeks ago, so you’re missing over two and a half years of development.
How important those development changes are depends on your use case. For DFT properties, the most important ones are bringing our UHF/UKS second-order properties up to par with our RHF/RKS ones, and some technical changes to our DFT integration procedures. I’m not a DFT developer, so Holger would know more than I would about the numerical integration tweaks.