So a changing room is considered a public place in the Quran.

Maybe you the interpretation of the referrals has been overdrawn a bit. Equally, at times of Quran there were no sports-clubs, health clubs and such (maybe bath-houses) thus it is one of these points where Quran is holding you in a position where flexibility and adaptation to current times are extremely difficult. Your deserts are changing into cities, this has consequences. CHANGE is one of them, change does not means you have to loose your faith or set aside core values, however whining over seeing a penis Tis just simply immature.