(15) (a) where an owner combines two or more vacant housing accommodations or combines a vacant housing accommodation with an occupied housing accommodation, such initial rent for such new housing accommodation shall be the combined legal rent for both previous housing accommodations, subject to any applicable guideline increases and any other increases authorized by this chapter including any individual apartment improvement increases applicable for both housing accommodations. If an owner combines a rent regulated accommodation with an apartment not subject to rent regulation, the resulting apartment shall be subject to this chapter. If an owner increases the area of an apartment not subject to rent regulation by adding space that was previously part of a rent regulated apartment, each apartment shall be subject to this chapter.
(b) where an owner substantially increases the outer dimension of a vacant housing accommodation, such initial rent shall be the prior rent of such housing accommodation, increased by a percentage that is equal to the percentage increase in the dwelling space and such other increases authorized by this chapter including any applicable guideline increase and individual apartment improvement increase that could be authorized for the unit prior to the alteration of the outer dimensions.
(c) notwithstanding subparagraphs (a) and (b) of this paragraph, such increases may be denied based on the occurrence of such vacancy due to harassment, fraud, or other acts of evasion which may require that such rent be set in accordance with section 26-516 of this title.