It´s an almost impossible task (but it´s always nice to be inspired and to inspire others to listen to what you think is great), and I´ll probably forget some albums, which deserve a place here, but I´ll give it a try:
Macabre - Dahmer (not strictly a death metal release, but Macabre are mostly accepted as death metal).
Morgoth - Odium (I know most people would mention "Cursed" instead of "Odium", but I love the post-apocalyptic atmosphere of Odium).
Pestilence - Testimony of the Ancients (it could also have been Consuming Impulse. I love that album too)
Atheist - Unquestionable Presence (today it´s probably not counted as death metal, but back then it was considered a weird jazzy form of death metal)
Carcass - Necroticism
Autopsy - Mental Funeral
Darkthrone - Soulside Journey (I´m not a huge fan of their black metal releases, but their death metal debut album...hell yeah)
Entombed - Clandestine
Dismember - Like an Ever Flowing Stream (which is the only Dismember album I´m interested in. The rest are sub par to this one).
Morbid Angel - Blessed are the Sick (could have been Altars of Madness or Covenant too, but Blessed...always thrilled me a bit more)
Benediction - The Grand Leveller
Bolt Thrower - ...for Victory (could have been a few of the others too)
Napalm Death - Harmony Corruption (their only "true" death metal album)
Deicide - Deicide (the debut album had a huge impact on me when it was released. Sadly they were never able to follow it up with something of equal or better quality).
Death - Human (could have been Symbolic too)
Edge of Sanity - Unorthodox
Bloodbath - Nightmares Made Flesh
Suffocation - Pierced from Within
Dying Fetus - Destroy the Opposition (all their albums are great, but this one and the predecessor are the strongest IMO)
Obituary - The End Complete (Obituary are incredibly consistent in style and quality, but this album is just a notch above the rest IMO).
Black Breath - Slaves Beyond Death (this album deserves far more attention than it has gotten. Had this been released in the early 90s, it would have been a death metal hit).
Atrocity - Hallucinations (this one seems like it´s been forgotten by time, and the fact that Atrocity changed their sound drastically throughout the years probably hasn´t helped either. If you haven´t heard of this album already, give it shot. It´s killer technical death metal with a great concept story).
Cynic - Focus (well not strictly a death metal release, but it was considered part of the scene back then)
Decapitated - Nihility (I love Organic Hallucinosis too. Vogg´s riffs floor me everytime I listen to Decapitated)
Nile - What Should Not Be Unearthed (could have been a few others too)
Malevolent Creation - The Ten Commandments
Opeth - Blackwater Park
Zyklon - World ov Worms
OK, I know that was a few more than 15, but this is probably my favorite style of music, so I couldn´t help myself.