In bulgarian present tense, the only possible form of the verbs is the imperfective one. So, in this sentence, undoubtly, the respective verb in singular would be "спомням си".
However, in all other uses ( like an infinitive, in future tense, etc.), since the plural 3rd person form "спомнят" is the same for perfect and imperfect, it is not possible to make any difference. (especially for this verb and its 3rd p. form in particular!)