You need to believe Paul's gospel to be saved.
1Co 15:1 Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand;
1Co 15:2 By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain.
1Co 15:3 For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures;
1Co 15:4 And that he was buried, and that he rose again the third day according to the scriptures:
The following is just me reacting off the top of my head to your quite bare statement. It should not be understood to be me accusing you of anything. Indeed, I'd be surprised to discover that you disagree with a syllable of what follows...
I entirely agree with this in principle and as stated it is quite correct, but we should be careful not to imply that a person must understand dispensational distinctions in order to be saved. He does not.
To be saved, a man must first believe that there is a God, and not merely some vague Power behind the universe, but the God who made it: the living Creator, holy, perfect, and just. He must also understand that he himself is not merely an imperfect creature in need of improvement, but a rebel. He has done evil against the One from whom he received his life, and therefore stands in need not simply of instruction or reform, but of rescue.
The Christian claim is that God Himself provided that rescue. Unwilling that men should perish, He entered His own creation as the man Jesus Christ. He who had no guilt of His own took upon Himself the guilt of others and died on their behalf. He then rose again from the dead.
That is the thing to be believed and the Person to be trusted. The sinner must acknowledge that he needs a Savior, confess Jesus Christ as that Savior, and believe that God raised Him from the dead. He is not being asked merely to admire Christ, nor merely to agree that Christianity contains many true things. He is being asked to entrust himself to the One whom God has provided for his salvation. And the promise attached to that faith is that he will be saved.
Now, that does indeed happen to be Paul's gospel. Large portions of what I have just described would scarcely be Christian doctrine at all apart from Paul's writings. So, in that sense, you are quite correct: it is Paul's gospel that must be believed.
But that is a very different thing from saying that a person must understand Paul's ministry dispensationally in order to be saved.
Millions upon millions of Christians throughout the world believe what I have just described while seeing no meaningful distinction at all between Paul's ministry and Peter's. Some believe the Church began at Pentecost, some at the Cross, some in Acts 9, and still others in Acts 28. Some understand grace remarkably well and go through life motivated chiefly by the love of God. Others, probably most, are up to their necks in legalism and are motivated far more by fear of judgment than by grace. There are, in short, hundreds of varieties of Christianity and an almost endless variety of Christians.
My point is simply this: a man may be wrong about a great many things and still be right about the thing upon which his salvation depends. If he understands who God is, understands his own guilt and need of salvation, and trusts in the crucified and risen Christ as the Savior God has provided, then he will be saved, even if much of the rest of his theology is held together with baling wire and duct tape.