Yes, 16K will have an impact, especially in 16bit or float. Many years ago, a real problem to load, especially when an HDRI had to work as background as well, then perhaps more than 32-64K to get sufficient data in the camera view. Which sometimes leads to manually resampling the image for what is needed.
I will run some tests with the current release and then file a report. Fingers crossed, it will help.