The phrase "more longtime" implies a length of time that has already passed, and the need for additional time. Synonyms for this phrase include "further long-standing," "protracted," "extended," and "continuing." Other options include "ongoing," "persistent," "enduring," and "chronic." These words all suggest a duration of time that is considerable, and may require patience or perseverance. If you are looking to express the idea of a long, ongoing period of time, any of these synonyms could be a good fit. Consider the context of your sentence and choose the word that fits best.