The Tac-Rigs I used made it much easier, because there are so many rockets and grenades that will come your way, and it prevents any enemy from coming too close to you. In the later rounds, watch out for snipers that are on the highest level where the orb is, and take them out first. When you get to round 8, you'll encounter a large robot, which you'll need to shoot quite a bit before firing rockets at it, and repeating until it's dead. When they're all done, rush to activate the next round and refill your ammo. Simply take down all enemies from where you started the round, and when you need to reload, use the supply box next to you, because it's faster. Start the rounds as soon as you can every time to get a bigger time bonus.

Note that for 'Personal Decorator', one of the medals requires you to complete all Campaign challenges, and one of those challenges is to pass all 16 rounds on Realistic difficulty, and there's another medal that requires you to get at least 35000 points. Set the difficulty to Recruit beforehand. You'll get time bonuses for finishing each round as quickly as possible. I got it at the end of round 14, and it took me just over 15 minutes to do. You don't necessarily need to beat all 16 rounds, depending on how good you are. To get gold you'll need to get at least 27500 points. The combat immersion is in the safehouse.

Black ops 3 combat immersion