You would have to make a rectangular pattern and suppress some of the elements or occurrences. (Patterns are made up of elements in an assembly but they are called occurrences in a part.)
Starting with your example you would make the pattern along the long edge of your plate with 11 columns then down the short edge with 2 (or more) rows and then suppress the last elements up to where you have your 15 or 16 or whatever.
I do not think you can control how many parts get suppressed with a parameter though. [I was thinking maybe you could do it in an iPart but it looks like you can only suppress or compute the entire pattern.]
Here's an attempt at something similar:
https://forums.autodesk.com/t5/inventor-programming-forum/suppress-pattern-occurrences-in-assembly/t...
This one starts out as something else but may have some suggestions and links that could get you pointed in the right direction:
https://forums.autodesk.com/t5/inventor-forum/how-to-suppress-the-last-and-first-element-of-a-patter...