“At that time I pleaded with God, saying...”
There is an angel appointed to watch over prayers, and he brings them up from the Earth to the Heaven, in a spiritual journey of 500 years. The angel does this with the power of two letters in God's name, yud and hey, and it was with these letters that God created the world. The 500 years plus the letters yud and hey gives 515.
These angels are described as “their legs were straight (ישרה),” which has a numerical value of 515. This is why Moses said, “I pleaded (ואתחנן)” - which also has the numerical value of 515 – that Moses pleaded with the angels to bring up his prayer (תפלה) - which again has a numerical value of 515. “At this time” means at the time when the prayers go up with the help of the angels, who do this with the letters yud and hey.
Art: Salomon de Bray - Jacob's Ladder