Thank you for your post.
macOS Sierra 10.12 was released during the FileMaker Pro 15 time frame, and it is supported.
FileMaker Pro 14 was not tested with macOS Sierra 10.12.
Personally, I run FileMaker Pro 14 and FileMaker Pro 15 on my macOS Sierra 10.12.4 machine, and although I do not use FileMaker Pro 14 as much as FileMaker Pro 15, I have not encountered any major issue. Are you seeing one?
No problems I was looking to update to 10.12.3, but based on your comment I think I will go directly to 10.12.4.
I am on FMPA 15 almost exclusively now.