Changes: 
-Changed the names of two methods in GameFifteenEngine.cs: "proverka" -> "CheckIfCellIsValid"; "proverka2" -> "CheckIfInGoodOrder". 
-Changed the names of two fields and properties in HighScore.cs: "name" -> userName; "score" -> userScore; (No! It's not overkill... xD)
Suggestions: 
-Change names of these members (not necessity in my opinion, but hey...) every "matrix" in name of member will be change with "gameField".