「身なり」 is a noun meaning "clothed appearance." English phrases like "dress neatly" or "tidy oneself up" can be translated as
「[身]{み}なりを[整]{ととの}える」
in Japanese.
"OK, you can come in, I'm decent now." could be said
「はい、[入]{はい}っていいですよ。[身]{み}なりが[整]{ととの}いましたから。」
or
「オーケー、入っていいよ。身なり整ったから。」
However, 「身なりを整える」 sounds somewhat formal. So, the example expressions which other users have suggested in the comments are more common in casual conversations.
In [浴衣]{ゆかた} and [着物]{きもの} dress worlds, 「[着姿]{きすがた}」 is a noun meaning "dressed appearance." But this word seems not to fit your context.
Sometimes, [着衣]{ちゃくい} is used as an antonym of 裸 in some contexts, although the official antonym of 着衣 is 脱衣. In the porn world, 着衣 seems to be an antonym of 全裸. However, 着衣 itself is a formal word. "Fully-clothed swimming" is called 着衣水泳 or 着衣泳 in Japanese. Anyway, 着衣 may be too formal to fit your context, but it's a possible word in some situations.
In colloquial Japanese, many people use 「[見]{み}せられる[格好]{かっこう}」 to express a clothed appearance. For example,
(knock, knock)
Clothed [涼太]{りょうた}「[美咲]{みさき}ちゃん、[迎]{むか}えに[来]{き}たよ。ドア[開]{あ}けて。」
Half-naked [美咲]{みさき}「あ〜〜まだ、[見]{み}せられる[格好]{かっこう}してない。ちょっと[待]{ま}って。」
Clothed 涼太「いいよ、[俺]{おれ}、そーゆーの[気]{き}にしないから。[開]{あ}けて。」
Half-naked 美咲「わたし、[気]{き}にするから。もうちょっとだけ[待]{ま}って。」
「[人様]{ひとさま}に[見]{み}せられる[格好]{かっこう}ではない」 is a common phrase of 見せられる格好. Tweets on Twitter may not be good examples of it, but, people use this phrase like these: tweets containing 見せられる格好.
「見せられない格好」 can mean not only [裸]{はだか}, but also various embarrassing appearances. So, 見せられる格好 is not a perfect opposite of 裸. But the expression 見せられる格好 may be useful in some situations in real life.
Clothed / Unclothed Group of People
I think that there are many words which can be antonyms or quasi-antonyms of 「裸の[人々]{ひとびと}」 in various contexts.
When a noun is used to describe a group of clothed people, what kind of clothes the people wear is usually specified in Japanese. For example,
[普段着]{ふだんぎ}の人々/ [正装]{せいそう}の人々 / [制服]{せいふく}の人々 /
[和服]{わふく}の人々 / [洋服]{ようふく}の人々 /
[厚着]{あつぎ}の人々 / [薄着]{うすぎ}の人々 / [半袖]{はんそで}の人々 / [青]{あお}い[服]{ふく}の人々 etc.
Hope that helps.