You can't say whether a facility has too many horses based simply on a number. You need also to know how much space they have. If they do have 90 acres, then I don't think 17 is too many at all. That should be plenty of room.
Given time, your horse should adjust just fine. Horses are herd animals and there is a hierarchy--after a couple of days, horses usually figure out their spot in the hierarchy and things are good.
I hope this answered your question~
The sensitivity of the internet baffles me.