A foreigner cannot apply for Indian citizenship just after marrying an Indian. However it is also not true that one has to wait for 15 years. The correct position presently is that one has to ordinarily stay for 7 years in India to apply for citizenship to the government of India.
The Indian Citizenship Act provides that a person married to an Indian should stay in India for 7 years marriage with the Indian spouse to make an application. The foreigner is required to fill Form III available on the website and certain formalities have to be complied with. The Citizenship Act also uses the term ‘ordinarily stay for 7 years’. In this regard the term ‘ordinarily stay’ means that the person must be in India for the entire 12 months before making the application. Therefore, a person applying for citizenship must show that he/she was in India in the preceding 12 months and an aggregate of 6 years before that. This means that the stay of six years can be scattered over a longer period of time and need not be cumulative like the requirement of 12 months.
Hence the Russian has to stay for another 4 years before she can apply for the citizenship. Also presently the government is considering relaxing the norms for registration of citizenship by foreigner married to Indians and the need to continuously stay for 12 months might be relaxed.
Section 5(c) of Indian citizenship act, 1955