It doesn't matter. Despite self-publishers touting this as a die-hard rule. It is not. And I think you mean odd pages (or recto or right side pages). The only chapter opener that absolutely must fall on an odd page is the first chapter. However, there are even exceptions to that, but none you would likely come across.
So, I basically did a bunch of research on this. It is a style preference that is determined by the series, brand, author, publisher, what have you. There are only conventions in print formatting and when conventions don't work, ignore them. It's more important you understand the reason of the convention then following the convention.
In most cases where chapters start on both sides of the page, there are clear signals letting the reader know she is in a new chapter. If the chapter opener doesn't have clear signals, one signal can be a right side page for chapter starts. If you're interested in lowering your page count, I recommend doing two things, drop your font size by half a point (adjust leading as necessary) and start chapters on both sides of the page. More often than not, you'll loose at least 15 pages, if not more (depending on your page count and other settings).
I might be reading between the lines here, and completely misreading, are you wanting to lower your book's page count? If so, there are bunch of things you can do (including starting chapters on both sides of the page) without sacrificing the readability, legibility, and comfortable margins.
