Is it obligatory to make up prayers intentionally missed due to laziness, knowing that they were missed for approximately three months, and the age is 14 years, and there is hardship in making them up; and is it sufficient to be diligent in performing the Sunan (supererogatory prayers) and to maintain current prayers?

If you abandoned prayer while young and not yet an adult, there is no sin upon you and no need for make-up prayers, because you were not accountable. However, if you abandoned it as an adult, then making up the prayers is obligatory, and this is the more cautious of the two opinions. If you are prone to religious scruples (waswās), then there is no harm for you in taking the concession of the other opinion. Since you are a layperson and young in age, you must emulate (taqlīd) someone among the people of knowledge whom you trust.