New Photos are surprisingly slow, comparing to Aperture interface and real time editing.
I cannot confirm this. It may depend on the model of your computer. For me, on a MacBook Pro Retina (late 2015) Photos is faster than Aperture has ever been. The first week Photos may be slow because of the heavy background processing. Photos is doing image analysis and classifying each photo into categories.That requires a lot of processing power during the initial migration, if the library is large. But it is worth it. When it is done, you can search for photos showing a beach or a sunset, a bear, or a squirrel without having to add keywords to the photos. Photos can recognize animals, people, landscape by analyzing the photo in combination with the location data.
The problem is more, that Photos does not allow us to customize the work space like we could in Aperture, and that the support for batch processing and metadata is very limited. For example, we cannot copy adjustments to a batch of photos, only onto individual photos. There are no presets to handle metadata. It is simply not a workspace for professional photo work .