How strange... I've lived in New Zealand my whole life, and never heard much about that kind of talk here - except when it comes to kids/teens who obviously have outgrown their ponies. I'm 5'4 and overweight and ride both a 15hh and a 14.2hh, but only ever had comments about the length of my old 16.1hh gelding's back to my weight and "breaking" him... albeit that started from a not so pleasant member on here actually. Further, my height matches my ponies, and again... only had the comments about my weight, or their weight, not anything else.
Where abouts in NZ are you, north or south? I'm in Christchurch, and I can't say I know of many people worried about height at all here... considering I know a few people who are slender and tall on 15.1-15.2hh horses and compete well etc.
Personally, if you feel comfortable, and you fit the horse well (height isn't everything, the size of the barrel and other parts of the horse's conformation can take up some leg, or lengthen it etc), then who really cares? As long as it's not an inconvenience for yourself or the pony, I don't find height ratios as big of an issue as you've otherwise experienced!
♥ Seoul Searchin' for the Lovebug ♥