Why is the date of the 2016 Passover a month late when compared to Easter? Jesus was put to death on Passover eve Nisan 14.

This was the first full moon following the vernal equinox.this year the vernal equinox is March 20.2016
The first full moon after March 20 is March 23 2016.  

This is the day that Jehovah's  Witnesses will have their annual memorial of Christs death event.

That is why those who celebrate Easter  will be doing so on March 27 2016. The first Sunday following the paschal full moon. 

All seems to be in order until I check the date for Passover this year and it is April 22 2016.

Can someone explain why there is almost a full month lag for Passover this year?
Jehovah's Witnesses time their Memorial  based on the current apparent movements of the actual physical moon and sun, as observable from Jerusalem. This, they say, is what happened in first century Judaism.  The rule is not exactly the first full moon following the equinox, but the result is very close to this.
Jews and Christians base Passover and Easter, respectively, on mathematical models of how the moon and sun move. These idealised models were calculated in the 4th century AD. They are somewhat out of step with the real moon and sun, used by JWs.
The result is that the assumed date of the Vernal Equinox has drifted later than the actual date. The earliest date  Passover can now fall is March 26th. The Full Moon on March 23rd, 2016 is too early for this, and so Passover is based on the following Full Moon, in April. This drift is continuing, but very slowly. Passover was on March 26th in 2013, and will again be on March 26th in 2089, and then never again. After that March 27th is the earliest. The last ever March Passover, based on current arrangements, will be March 31st 3248. In 3411, Passover will fall in May for the first time.
In Christianity the situation is complicated by the fact that Western Christians have made adjustments to correct the drift of sun and moon dates, so that the idealised sun and moon correspond more accurately to the real ones. Eastern Orthodox Christians have not. The drift is such that the earliest the Paschal Full Moon can fall, according to the Eastern Church, is April 3rd. Just as for Jews, the March 23rd full moon this year is too early to be counted, and so it is the April Full Moon is regarded as the Paschal one.
Western Christians have made adjustments so that the earliest date the Paschal Full Moon can fall is March 21st, close to the real vernal equinox. Therefore the March 23rd Full Moon does count and so Easter Day is the following Sunday, March 27th.
Apart from the month, the actual  assumed dates of full moons can vary by a day or two from the real ones for both  Jews and Western  Christians.  For Eastern Christians the ideal  full moon occurs 4 or 5 days later than for Western Christians.
So for 2016 there are full moons on March 23rd and April 22nd. The Jehovah's Witnesses Memorial is on March 23rd. Western Easter is the following Sunday, March 27th. Passover is the following full moon, April 22. The Eastern Orthodox model full moon is four days later than this, April 26th, and so Orthodox Easter is the Sunday after this, May 1st.
Fort the whole of this century if we divide the year AD by 19, and the remainder is 2, 10 or 13, then Passover will be about a month later than Western Easter.   If the remainder is 2, 7, 10, 13 or 18 then the Eastern Easter will be 4 or 5 weeks later than the Western one. In other years, if the Full Moon is early in the week, Eastern and Western Easters coincide, but if later in the week the Eastern Easter is one week after the Western, as the 4 or 5 day discrepancy pushes the assumed full moon into the following week.