Tyre had become proud and full of self glory. God apposes those who glorify themselves with their wealth.
According to Ellicott's Commentary for English Readers
(Tyre shall be forgotten seventy years (verse 15)--If we take the number literally, the seventy years may coincide with those of the captivity of Judah, during which, under the Chaldaean supremacy, Tyre was reduced to a state of comparative insignificance. It seems better, however, with Cheyne, to take it as a symbolic number for a long period of indefinite duration, and so, bringing it into closer connection with the context, to reckon the period from its conquest by the Assyrians.
At the end of seventy years, the Lord with deal with Tyre (verse 17) - The Hebrew word used for "deal" can also be translated "visit, restore ". By Acts 21:3-4, we see that there were Chrsit followers in Tyre.
2 Chronicles 36:15-23 describes "The Fall of Jerusalem" at the hands of the Babylonians. These verses also show the restoration of Jerusalem at the hands of the Persions "in order to fulfill the word of the Lord".
2 Chronicles 36:20- 23
20 He carried into exile to Babylon the remnant, who escaped from the sword, and they became servants to him and his successors until the kingdom of Persia came to power. 21 The land enjoyed its sabbath rests; all the time of its desolation it rested, until the seventy years were completed in fulfillment of the word of the Lord spoken by Jeremiah.
22 In the first year of Cyrus king of Persia, in order to fulfill the word of the Lord spoken by Jeremiah, the Lord moved the heart of Cyrus king of Persia to make a proclamation throughout his realm and also to put it in writing:
23 “This is what Cyrus king of Persia says:
“‘The Lord, the God of heaven, has given me all the kingdoms of the earth and he has appointed me to build a temple for him at Jerusalem in Judah. Any of his people among you may go up, and may the Lord their God be with them.’”