Exodus 14:15

And the Lord said to Mosheh, Why standest thou praying before Me? Behold, the prayers of My people have come before thy own: speak to the sons of Israel, that they go forward;

There are those who say that Moshe was screaming out to Hashem. This is not correct, since He already spoke to him when saying ואכבדה בפרעה. [Rather] it [the text] only speaks of Moshe, who is representative of all of Israel. [This was] because Bene Yisrael screamed out to Hashem [14:10]

AND THE ETERNAL SAID UNTO MOSES: WHEREFORE CRIEST THOU UNTO ME? Rabbi Abraham ibn Ezra commented — teaches by implication that Moses had been praying. Ibn Ezra’s explanation is first in the text, and Ramban’s interpretation follows it. that Moses corresponds in function to all of Israel who were praying to G-d, as Scripture said, And the children of Israel cried out unto the Eternal. But if so, why did G-d say, Wherefore criest thou? When it was indeed proper that they should pray! Perhaps [Ibn Ezra] will say that the sense thereof is: “Why do you let them pray? Speak to them so that they will go forward, for I have already told you, And I will be honored through Pharaoh.”
And our Rabbis have said that it was Moses who was crying and praying. This is the correct interpretation [and not, as Ibn Ezra said, that the reference here is to all of Israel]. Moses was at a loss concerning what he was to do. Although G-d had told him, And I will be honored through Pharaoh, he did not know how to conduct himself at that moment when he was at the edge of the sea and the enemy was pursuing and overtaking [them]. He therefore prayed that G-d should instruct him in the manner that he should choose. This then is the meaning of Wherefore criest thou unto Me? meaning: “You should have asked what to do, and there is no need for you to cry, since I have already informed you, And I will be honored through Pharaoh.” Now Scripture did not relate that Moses was crying out to G-d, because he is included among Israel, [of whom it was already written above in Verse 10: And the children of Israel cried out unto the Eternal].

מה תצעק אלי?; G’d’s question seems at first glance redundant, seeing that Moses’ outcry could have been perceived as part of the nation’s outcry in verse 10, i.e. ויצעקו בני ישראל וגו'.However, Moses’ outcry had nothing to do with being afraid of the pursuing Egyptians. He had already predicted the downfall and death of Pharaoh and his army as being so decisive that Egypt as a world power would never again pose a serious threat to the Jews. (verse 13-14) He had also told the people that G’d would do the fighting for them and that all they had to do was to remain silent. Moses’ outcry was one of concern with the rebellious attitude of the people who not only were afraid, something that could be forgiven, but who had dared to be sarcastic in their hour of danger, ridiculing Moses’ leadership to the point where he was afraid that they would refuse to enter the sea when told to. G’d told Moses that he had no right to assume such a thing, that in fact he was suspecting innocent people of lack of faith.

דבר אל בני ישראל ויסעו, G’d is challenging Moses to issue the order to move forward, assuring him that he will see immediately that the people will respond positively.