Does anybody know any good 11-15 episodes anime?

No. 6 (Unless bạn don't mind two little pecks on the lips bởi two males throughout the whole anime)
Air
Shinrei Tantei Yakumo
WataMote
Amnesia

Diabolik những người đang yêu 12 eps.
link

No.6
K (the pic)
Karneval
Kamisama Hajimemashita
Tonari No Kaibutsu Kun
Kuragehime
Tsuritama
Noragami
Acchi Kocchi
Amnesia
Diaobolik Lovers
Ano Hana
Hoozuki No Reitetsu

Here's a few good ones with 11-13 episodes:
High School DxD/New
Spice + Wolf//II
Marvel Anime: Blade, Wolverine, X-Men
Date A Live
Infinite Stratos/II


These are the only good anime I can think of with 11-13 episodes.

Baka and Test (picture) & Serial Experiments Lain are amazing.
Watch Baka and Test for fun and comedy.
Watch Serial Experiments Lain for a weird anime that not one person can truly look at the same.

Noragami
Highschool DXD
Kamisama Kiss
Elfen Lied
Mayo Chiki (pic）
11eyes
Freezing
A Dark Rabbit has only Seven Lives
Kore wa zombie desu ka?
Mahou Sensou
Heaven's Mất tích Property
Princess Princess
Otome wa Boku ni Koishiteru