"I have been living in the UK since I was 15." "I have lived in the UK since I was 15." These two sentences have basically the same meaning. Because this example has the phrase "since I was 15," either "have lived" or "have been living" is acceptable, because "since I was 15" tells us that the action started in the past and continues to the present. You can also use the past participle form after the word "been" in sentences that use the passive voice. "She has been seen by the doctor." (The doctor saw her.) (see-saw-seen) "The money has been hidden in this room." (Someone hid the money in this room.) (hide-hid-hidden) "I have been hit by a ball." (A ball hit me.) (hit-hit-hit) "We have been tricked!" (Someone tricked us!) (trick-tricked-tricked) You can also follow "been" with a preposition to describe a past location. "I have been to the United States." "She has been in his house." "Squirrels have been on my roof."

No, it's not compulsory, using your example, you could say "I have been in the UK since I was 15." Saying "I have lived in the UK since I was 15" or "I have been living in the UK since I was 15" are ok, too.

No it is not necessary.