Smoking is low and slow. Unless you want to eat it raw 15 minutes will barely get the outside warm at 270. Smoking is meant to take tough cuts of meat and make them tender through low heat and time. I think what you would want to do with a top sirloin is grill it, preferably over coals.
Ceramic grills are wonderful if your serious about your grilled meats. I have a Primo Jr. which is ceramic like a Kamado and many others like that.
The advantage of a ceramic grill is you can get it very hot, up to 600-700 degrees. You can take a steak, brush veg oil all over it and flash fry it on the grill at those temps. You can also cook low and slow. They retain their heat like no other cookers. One of the great things about them is your meats stays much more juicy cooking on a ceramic.
The disadvantages are you must use charcoal. Lump is preferable. Absolutely no wood allowed. It gives off a smoke that permeates and ruins the ceramic. Same with liquid fire starter fuel, that's a big no no because it will permeate the ceramic and you'll never get the odor out. So use a propane torch starter or a charcoal chimney. Also, for a low slow long cook, when you want to add more coals you have to remove all your food, pull the grates off and add your charcoal. Thankfully you don't have to do that often because they burn lump charcoal for a very long time.
Like I said above, I love it for thick cut pork chops, or any pork chop really, Lamb chops and Veal chops, and small roasts. The meat stays so juicy. You put your coals on one side. Sear your meat off for 3-5 minutes at about 400 degrees over the coals then move it to indirect heat on the other side. Give it 10-20 min, depending on what it is, and it will be perfect. If you have the money and want to grill your butt off I highly recommend one. I prefer the Primo's because they are oval shaped and that shape lends itself well to grilling direct to indirect. The thickness of the ceramic is the same as a Kamado, and it cooks just as well, it's just a better shape IMO.