If one has 2 hours to say Tehillim, Is it better to say all of Sefer Tehillim quickly but with no interruptions or is it better to recite half of it or part of it slowly and carefully (without interrupting)?

There is a special benefit in reciting all of Sefer Tehillim. That said, one can complete reading Tehillim in one sitting, over the course of the week, or over the course of the month. It is preferable to recite the Tehillim accurately, with understanding of the meaning of the words being recited and with "Kavanna" [=intent].