I have an older machine and can support 15 (have not bought yet) but I need to be able to import and edit mpeg4 video for the project I have in mind. I plan to upgrade to 17 after I get a new PC, but not for a while.
If I am not mistaken, MPEG-4 can have a proprietary codec, so even if someone says yes, they can import theirs, it doesnt mean you will have the same success.
As a test, I opened my MEP 15, took a video that I had, exported it to MPEG-4 and then closed, re-opened the program and imported the MPEG-4 video... but again, this does not mean that all mpg4 video works.