macbook 2015 13 ssd pcie dilemma

The OWC Aura SSDs are the only ones which I know for sure are a drop in replacement not requiring an adapter. I have seen some people mention Transcend on these forums, but I have no idea if they offer a native solution or provide their own adapter. Nor do I know what their SSDs may be like. I doubt you will find any other drop in replacement SSDs due to the proprietary Apple connector and the very limited market for it.

An M.2 SSD will always need an adapter to work internally on a Mac since Apple uses a proprietary non-standard PCIe SSD connector and an M.2 SSD is the standard all other vendors are using since Apple unfortunately "Thinks Different".

I don't know about the compatibility issues with the various Samsung SSDs. I do know the vast majority of the SSDs Apple uses are made by Samsung. An M.2 SSD like the Samsung SSDs require the use of an SSD adapter. It appears the Sintech adapter has the best feedback for compatibility & reliability compared to any other brand of adapter.

Keep in mind any standard M.2 SSD will have no support from the SSD manufacturer since you are using the SSD on an unsupported computer which requires a third party adapter which introduces even more possibilities for issues.

At least the OWC Aura SSDs do not require an adapter and they have support provided for them by OWC.

As for any speed differences you are unlikely to notice except with certain workloads. No matter what an NVMe SSD will be faster than the current Apple PCIe SATA based SSD from the factory (assuming you get a decent SSD). This article reviews the Aura X2 and gives a brief mention of the N2:

https://www.anandtech.com/show/14382/the-owc-aura-pro-x2-ssd-review-nvme-for-older-macs/9

Go with the SSD you feel most comfortable with as it is your laptop and you must be happy with it. If you have a replacement battery, then any battery consumption issues should not really matter if they even exist as I cannot see it would be that significant. A lot of the PCIe SSDs tend to get hot. I've even caused an original Apple SATA based PCIe SSD to overheat during a stress test. If you go with a standard M.2 SSD I think the Sintech adapter is the most important part of the equation. I've never used a standard M.2 SSD in a Mac so perhaps there are other acceptable adapters. Sometimes it is easy to over think things too much (I know I'm guilty).

Keep in mind your laptop needs to be running macOS 10.13+ before you can even install the third party NVMe SSD since the macOS 10.13+ installer updates the system firmware to work with an NVMe SSD. You will also need to install & use macOS 10.13+ since older versions of macOS don't have the NVMe driver necessary to work with a third party NVMe SSD. I highly recommend you keep the original Apple SSD just in case it is ever needed.