I would like to help you, so let's try from another point of view:
1) What error your iPhone 15 is giving you? (you say video 'it won't start', but more details are appreciated). If video displays only a black screen, you could try disabling 'GPU Process: Media', following this instructions
HERE. But before doing any changes on your iPhone configuration, it would be great if you could upload here (on the forum) the logs of your video player. Check
HERE to get instructions on how to get the logs, or see here:
How do I view Safari log on iPhone?2) What app are you using to play the videos? (native Safari player?)
3) Could you (temporary) try running HFS on standard port 80? instead of using port 32365 (perhaps your iOS player doesn't like playing videos on non-standard ports)
4) How about adding this (in your events file):
[download]
{.add header|Connection: keep-alive.}
{.add header|Keep-Alive: timeout=60.}
Your iPhone should give you some clue of why don't like to play the video...