Will the battery cycle go to 0 if I reset my iPhone 15?

No, of course it won't. The battery cycle count is a count of how many times it has charged fully. Resetting your phone cannot restore the battery to it's out of the box condition. And as already suggested, Battery Health goes only one direction and that is down. If your goal in resetting your iPhone is to restore the battery to 0, it won't work, so a wasted effort entirely.

I very much doubt it. I don't know what you mean by "reset" but likely the battery count is something that requires resetting as part of battery service.

Will it go back to 0 if I factory reset it?

No, but even if it did....the difference would not be significant.

Maybe if you could tell us what you are trying to accomplish, we might be able to help.

Your iPhone battery health only goes in one direction, down.

Don’t worry about your battery health so much. Your battery health is expected to drop about 1% or 25 charge cycles a month, and the decline isn’t linear. Meaning some months you may lose more than expected, or other months none at all. When it reaches 80%, have the battery replaced.

Okay. I thought you were asking about something like this —> Use Repair Assistant to finish an iPhone or iPad repair - Apple Support