Does anybody know any good 11-15 episodes anime?

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

Diabolik Lovers 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 {Picture}
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 Lost Property
Princess Princess
Otome wa Boku ni Koishiteru