Games built in Unity run slowly

I'm not sure it's as simple as that. Inside your build you could change to use DirecttX11 / 9, or 32/64 bit, etc. Any of these build options could effect performance.

Could we see the code for your 4 buttons and menu? Could be as simple as too many If statements acting against each other.

Sorry, but it's in Hungarian... And there are only three buttons and one picture.

 #pragma strict
 
 var Stilus : GUISkin;                    //Az Inspectorban szerkeszthető stílus
 var Hajtovadaszat : Texture;
 var Magassag : int = 250;                //A script által növelt változó, mely az elem helyzetét határozza meg
 var GombSzelesseg : int = 150;            //A gombok szélessége
 var GombMagassag : int = 50;            //A gombok magassága
 var Koz : int = 30;                        //Két gomb közötti hely nagysága
 private var Eloszor : boolean = true;    //Azt tárolja, hogy a script először van-e meghívva
 private var Pozicio : int = GombMagassag + Koz;
 
 function OnGUI () {
     GUI.skin = Stilus;
     GUILayout.BeginArea(Rect(0, Screen.height/2-300, Screen.width, 800));
         GUILayout.BeginArea(Rect((Screen.width/2)-(Hajtovadaszat.width/2), 50, Hajtovadaszat.width, Hajtovadaszat.height));
             GUILayout.BeginArea(Rect(0, 0, Hajtovadaszat.width, Hajtovadaszat.height), Hajtovadaszat);
             GUILayout.EndArea();
         GUILayout.EndArea();
         if (GUI.Button (Rect (Screen.width/2-GombSzelesseg/2, Magassag, GombSzelesseg, GombMagassag), "Játék indítása")) {
             Application.LoadLevel("Terkep");
         }
         if (GUI.Button (Rect (Screen.width/2-GombSzelesseg/2, Magassag + GombMagassag + Koz, GombSzelesseg, GombMagassag), "Instrukciók")) {
             Application.LoadLevel("Instrukciok");
         }
         if (GUI.Button (Rect (Screen.width/2-GombSzelesseg/2, Magassag + 2*(GombMagassag + Koz), GombSzelesseg, GombMagassag), "Kilépés")) {
             Application.Quit();
         }
     GUILayout.EndArea();
 }

Ehh I can't read Hungarian. I see the normal stuff, but I don't know what half the stuff is in English lol. And I'm not familiar with to much with Unityscript anymore.

Sorry I can't help much, but maybe somebody who can atleast piece together what the other language means and find an error in it.

Try doing a test and see if it runs slow.

Start a new scene and just put a plane with a box on top of it (of course with a camera looking at it)

See what the Frames are.

It also could be Vsync. Goto Edit > Project Settings > Quality and change the Vsync to None or off or whatever it is. (Ur frames will be way better than always) and it may or may not work better for the situation of your game as it can cause screen tearing.

I put a link for a setup file of my game, so you can have a look on it and how does it run. The first run is extremely slow, it's around a minute to start the game (the first button in the menu)...