Is Buddhism life denying or life negative?

Ok, do you believe rebirth is the cause of death or death the cause of rebirth? Sounds like the former. However the buddha was enlightened and he still died.

The ultimate cause of birth, death, disease and suffering is ignorance. Not rebirth. Not prevention of birth.

The way to end suffering is to end craving by ending ignorance through cultivation of virtue, concentration and wisdom.

For e.g. if you see a lot of foolish citizens who are not wearing face masks or social distancing in the time of the pandemic - the solution is not to prevent the birth of foolish people or to kill foolish people. The solution is to educate them.

Similarly, the solution to end suffering by ending craving and ignorance, is really by cultivating virtue, concentration and wisdom.

You can only end YOUR ignorance. You can help others reduce their ignorance. But there will always be ignorance somewhere. And because of that, there will be birth, death, disease and suffering.

Don't ask "whose suffering?", "whose craving?", "whose ignorance?"

Remember sabbe dhamma anatta - all phenomena is not self. There is suffering, not my suffering or your suffering. There is craving, not my craving or your craving. There is ignorance, not my ignorance or your ignorance.

One day, our Sun will grow hotter, expand and eventually explode. This will happen at least 5 to 8 billion years later. All life on Earth will eventually be destroyed.

But just as how life started on Earth through chemical interactions, it can start again somewhere on another planet. Perhaps it already has. With the start of life, followed by evolution, eventually, the mind will reemerge, and with it, ignorance will also return. With ignorance, we would have the birth, death and rebirth of sentient beings.

Rebirth here is the rebirth of ignorance, rebirth of the individual existence of a sentient being, and the rebirth of suffering. Not the rebirth of a specific countable and distinctively identifiable individual self that is permanent and standalone - that would violate the fact of anatta.

From SN 15.1 (translated by Ven. Sujato):

Transmigration has no known beginning. No first point is found of sentient beings roaming and transmigrating, hindered by ignorance and fettered by craving. For such a long time you have undergone suffering, agony, and disaster, swelling the cemeteries. This is quite enough for you to become disillusioned, dispassionate, and freed regarding all conditions.”

Or from another translation of this same paragraph in SN 15.3 (translated by Ven. Thanissaro):

“From an inconstruable beginning comes transmigration. A beginning point is not evident, though beings hindered by ignorance and fettered by craving are transmigrating & wandering on. Long have you thus experienced stress, experienced pain, experienced loss, swelling the cemeteries—enough to become disenchanted with all fabricated things, enough to become dispassionate, enough to be released.”

This stock paragraph is in most of the suttas of SN 15.

(Oddly, I am studying DN15 myself as of yesterday...)

Buddhism is not life denying and negative. Buddhism is craving denying and negative. Craving leads to suffering.

DN15:3.1: So: name and form are conditions for consciousness. Consciousness is a condition for name and form. Name and form are conditions for contact. Contact is a condition for feeling. Feeling is a condition for craving. Craving is a condition for grasping. Grasping is a condition for continued existence. Continued existence is a condition for rebirth. Rebirth is a condition for old age and death, sorrow, lamentation, pain, sadness, and distress to come to be. That is how this entire mass of suffering originates.

Your quote from DN15 is actually not denying life. Rather, it is part of a gentle discussion that guides the listener to this:

DN15:18.2: Suppose there were totally and utterly no craving for anyone anywhere.

Craving is the weak link in the chain of dependent origination and DN15 explores many nuances here (e.g., desire, lust, seeking, assessing, etc.). The other aspects of dependent origination keep happening. People keep being reborn. Contacts resume after immersion. Etc.

So my understanding of DN15 is that Buddhism affirms life and death without grasping at either. Denying and negativity are aversive dukkha.

DN15:18.3: That is, craving for sensual pleasures, craving for continued existence, and craving to end existence. When there’s no craving at all, with the cessation of craving, would seeking still be found?”

The Buddha did not deny or negate life. After his enlightenment, he lived content, without wishes in this very life. He lived a full life and taught for about forty years. And here, 2500 years later, the Buddha's teachings have eased my own life and brought happiness. Relinquishing craving and rebirth is not life denying and negative. Relinquishing craving and rebirth is affirmative of gratitude for all that we are given without greediness for more.

Why your question and all the other similar questions you linked are not getting a direct answer, but a shuffle is because the Buddha did not give an answer for such questions.

You may read many shuffles here, but the truth is questions such as Begining of life, end of life (i.e. beginner and end of Samsara); or hypothetical scenario in which all sentient beings attain Nirvana will receive a cold silence as an answer from the Buddha.