The date of Easter is determined by the first Sunday after the first full moon preceding the Spring Equinox. If this is the deciding factor for when Easter is celebrated then is it not in fact a Pagan celebration disguised as a Christian one?

Yes.

You may appreciate these quotes:

Confirming its pagan background, The Catholic Encyclopedia, edition of 1909, states in Volume 5, on page 227:

“A great many PAGAN customs, celebrating the return of spring, gravitated to Easter. The egg is the emblem of the germinating life of early spring. . . . The rabbit is a PAGAN SYMBOL and has always been an emblem of fertility.”

In harmony with this The Encyclopedia Americana, edition of 1956, states in Volume 9, on page 506: “According to the Venerable Bede, English historian of the early 8th century, the word [Easter] is derived from the Norse Ostara or Eostre, meaning the festival of spring at the vernal equinox, March 21, when nature is in resurrection after winter. Hence, the rabbits, notable for their fecundity, and the eggs, colored like rays of the returning sun and the northern lights or aurora borealis.”

“Children roll pasch eggs in England. Everywhere they hunt the many-colored Easter eggs, brought by the Easter rabbit. This is not mere child’s play, but the vestige of a fertility rite, the eggs and the rabbit both symbolizing fertility. Furthermore, the rabbit was the escort of the Germanic goddess Ostara who gave the name to the festival by way of the German Ostern.” – Funk & Wagnalls Standard Dictionary of Folklore, Mythology and Legend, edition of 1949, Volume one, page 335.

That the celebration finds no authorization in the Holy Scriptures or precedent among early Christians is pointed out by The Encyclopædia Britannica, eleventh edition, Volume 8, page 828:

“There is no indication of the observance of the Easter festival in the New Testament, or in the writings of the apostolic Fathers. The sanctity of special times was an idea absent from the minds of the first Christians. . . . The ecclesiastical historian Socrates (Hist. Eccl. v. 22) states, with perfect truth, that neither the Lord nor his apostles enjoined the keeping of this or any other festival . . . and he attributes the observance of Easter by the church to the perpetuation of an old usage, ‘just as many other customs have been established.’” The old usage was the practice of pagans to have a festival in honor of their goddess of spring.