I Corinthians 15:1-11 is NOT a statement of the Gospel. Paul simply is providing a list of four hallmarks whereby the Christian may ascertain whether a teacher is presenting the Gospel of the Scripture or a counterfeit of the Gospel. The four hallmarks are:
(1) Christ died for our sins according to the Scriptures.
(2) Christ was buried.
(3) Christ rose again the third day according to the Scriptures.
(4) Christ was seen of many witnesses.
The Gospel is the "glad tidings" or "good news" that the prophesied Kingdom of Heaven today is a reality, having been implemented the day, two thousand years ago, that Jesus was seated at King on the revived Throne of David. Included in the glad tidings are instructions whereby a man may gain entrance into the Kingdom, through the death of Jesus in the role of the Lamb of God. But the subject and heart of the Gospel is the Kingdom, which is to say, the prophesied Reign of the Christ.
The reason that the Kingdom is not apparent to most Protestants is the failure to understand that the operation of a government requires more than a king on the throne. The Kingdom of God has many officers, for the government which the Kingdom imposes is a comprehensive government which is global. The Kingdom regulates industry, commerce, education, and transportation.
Nor has Jesus been idle for the past two millennia. Jesus told his disciples that many offices (KJV "mansions") are in the government (KJV "house") of the God the Father, and that he would be preparing for them an office (KJV "place" or "room"), which is to say, a commission or enumeration of responsibilities. Design of a complex government is not a simple undertaking; as history demonstrates, the task of right governance is beyond human ability.
Meanwhile, despite the fact that Jesus today reigns as King, the offices of the Kingdom are vacant. And because the offices are vacant, Protestants think that the implementation of the Kingdom lies yet in the future; they expectantly await the "return" of Jesus, oblivious to the fact that Jesus returned two thousand years ago.
The Protestant does not understand that the offices of the Kingdom are to be staffed with the Justified, once the Justified have been resurrected from the dead. In the Resurrection, mortal, corruptible creatures of the Natural Realm are transformed into immortal, incorruptible beings of the Spirit Realm. Indeed, the Resurrection is the Second Birth, by which the Justified are born into the family of God. But at the present time, most of the Justified lie in the Grave, awaiting the Resurrection.
But vacant offices do not negate the present reality of the Kingdom and the present reality of the Reign of the Christ. The Gospel is the news that the Kingdom is a present reality, and that there still is opportunity to gain entrance into the Kingdom.